Methods for non-invasive prenatal ploidy calling

ABSTRACT

The present disclosure provides methods for determining the ploidy status of a chromosome in a gestating fetus from genotypic data measured from a sample of DNA from the mother of the fetus and from the fetus, and from genotypic data from the mother and optionally also from the father. The ploidy state is determined by using a joint distribution model to create a set of expected allele distributions for different possible fetal ploidy states given the parental genotypic data, and comparing the expected allelic distributions to the pattern of measured allelic distributions measured in the mixed sample, and choosing the ploidy state whose expected allelic distribution pattern most closely matches the observed allelic distribution pattern. In an embodiment, the mixed sample of DNA may be preferentially enriched at a plurality of polymorphic loci in a way that minimizes the allelic bias.

RELATED APPLICATIONS

This application is a continuation of U.S. Utility application Ser. No.14/446,232, filed, Jul. 29, 2014; U.S. Utility application Ser. No.14/179,399, filed Feb. 12, 2014; and U.S. Utility application Ser. No.14/100,928, filed Dec. 9, 2013. U.S. Utility application Ser. No.14/446,232 is a continuation of U.S. Utility application Ser. No.14/179,399, filed Feb. 12, 2014; U.S. Utility application Ser. No.14/100,928, filed Dec. 9, 2013; and U.S. Utility application Ser. No.13/110,685, filed May 18, 2011 (now U.S. Pat. No. 8,825,412). Utilityapplication Ser. No. 14/179,399 and U.S. Utility application Ser. No.14/100,928 are both a continuation of U.S. Utility application Ser. No.13/110,685. U.S. Utility application Ser. No. 13/110,685 claims thebenefit of and priority to U.S. Provisional Application Ser. No.61/395,850, filed May 18, 2010; U.S. Provisional Application Ser. No.61/398,159, filed Jun. 21, 2010; U.S. Provisional Application Ser. No.61/462,972, filed Feb. 9, 2011; U.S. Provisional Application Ser. No.61/448,547, filed Mar. 2, 2011; and U.S. Provisional Application Ser.No. 61/516,996, filed Apr. 12, 2011; the entirety of these applicationsare hereby incorporated herein by reference for the teachings therein.

FIELD

The present disclosure relates generally to methods for non-invasiveprenatal ploidy calling.

BACKGROUND

Current methods of prenatal diagnosis can alert physicians and parentsto abnormalities in growing fetuses. Without prenatal diagnosis, one in50 babies is born with serious physical or mental handicap, and as manyas one in 30 will have some form of congenital malformation.Unfortunately, standard methods have either poor accuracy, or involve aninvasive procedure that carries a risk of miscarriage. Methods based onmaternal blood hormone levels or ultrasound measurements arenon-invasive, however, they also have low accuracies. Methods such asamniocentesis, chorion villus biopsy and fetal blood sampling have highaccuracy, but are invasive and carry significant risks. Amniocentesiswas performed in approximately 3% of all pregnancies in the US, thoughits frequency of use has been decreasing over the past decade and ahalf.

It has recently been discovered that cell-free fetal DNA and intactfetal cells can enter maternal blood circulation. Consequently, analysisof these cells can allow early Non-Invasive Prenatal Genetic Diagnosis(NPD).

Normal humans have two sets of 23 chromosomes in every diploid cell,with one copy coming from each parent. Aneuploidy, a condition in anuclear cell where the cell contains too many and/or too few chromosomesis believed to be responsible for a large percentage of failedimplantations, miscarriages, and genetic diseases. Detection ofchromosomal abnormalities can identify individuals or embryos withconditions such as Down syndrome, Klinefelter's syndrome, and Turnersyndrome, among others, in addition to increasing the chances of asuccessful pregnancy. Testing for chromosomal abnormalities isespecially important as the mother's age: between the ages of 35 and 40it is estimated that at least 40% of the embryos are abnormal, and abovethe age of 40, more than half of the embryos are abnormal.

Some Tests Used for Prenatal Screening

Low levels of pregnancy-associated plasma protein A (PAPP-A) as measuredin maternal serum during the first trimester may be associated withfetal chromosomal anomalies including trisomies 13, 18, and 21. Inaddition, low PAPP-A levels in the first trimester may predict anadverse pregnancy outcome, including a small for gestational age (SGA)baby or stillbirth. Pregnant women often undergo the first trimesterserum screen, which commonly involves testing women for blood levels ofthe hormones PAPP-A and beta human chorionic gonadotropin (beta-hCG). Insome cases women are also given an ultrasound to look for possiblephysiological defects. In particular, the nuchal translucency (NT)measurement can indicate risk of aneuploidy in a fetus. In many areas,the standard of treatment for prenatal screening includes the firsttrimester serum screen combined with an NT test.

The triple test, also called triple screen, the Kettering test or theBart's test, is an investigation performed during pregnancy in thesecond trimester to classify a patient as either high-risk or low-riskfor chromosomal abnormalities (and neural tube defects). The term“multiple-marker screening test” is sometimes used instead. The term“triple test” can encompass the terms “double test,” “quadruple test,”“quad test” and “penta test.”

The triple test measures serum levels of alpha-fetoprotein (AFP),unconjugated estriol (UE₃), beta human chorionic gonadotropin(beta-hCG), Invasive Trophoblast Antigen (ITA) and/or inhibin. Apositive test means having a high risk of chromosomal abnormalities (andneural tube defects), and such patients are then referred for moresensitive and specific procedures to receive a definitive diagnosis,mostly invasive procedures like amniocentesis. The triple test can beused to screen for a number of conditions, including trisomy 21 (Downsyndrome). In addition to Down syndrome, the triple and quadruple testsscreen for fetal trisomy 18 also known as Edward's syndrome, open neuraltube defects, and may also detect an increased risk of Turner syndrome,triploidy, trisomy 16 mosaicism, fetal death, Smith-Lemli-Opitzsyndrome, and steroid sulfatase deficiency.

SUMMARY

Methods for non-invasive prenatal ploidy calling are disclosed herein.In an embodiment of the present disclosure, methods are disclosed fordetermining a ploidy status of a chromosome in a gestating fetus, themethod comprising obtaining a first sample that contains DNA from themother of the fetus and DNA from the fetus; obtaining genotypic datafrom one or both parents of the fetus; processing the first sample bypurifying the DNA so as to obtain a second sample; measuring the DNA inthe second sample at a set of polymorphic alleles; calculating, on acomputer, allele ratios at the set of polymorphic alleles from the DNAmeasurements made on the second sample; creating, on a computer, aplurality of ploidy hypotheses concerning expected allele ratios at theset of polymorphic alleles on the chromosome for different possibleploidy states of the chromosome; building, on a computer, a jointdistribution model for heterozygosity rates of each polymorphic alleleon the chromosome for each ploidy hypothesis using genotypic data fromthe one or both parents of the fetus; determining, on a computer, arelative probability of each of the ploidy hypotheses using the jointdistribution model and the allele ratios calculated for the secondsample; and calling the ploidy state of the fetus by selecting theploidy state corresponding to the hypothesis with the greatestprobability. In an embodiment of the present disclosure, the firstsample has been isolated from maternal blood. In an embodiment of thepresent disclosure, the step of processing the first sample furthercomprises amplifying the DNA.

In an embodiment of the present disclosure, the step of processing thefirst sample further comprises preferentially enriching the DNA at theplurality of polymorphic loci. In an embodiment of the presentdisclosure, the preferentially enriching the DNA at a plurality ofpolymorphic loci comprises obtaining a pre-circularized probe such thatthe 3′ and 5′ ends are designed to hybridize to a region of DNA that isseparated from the polymorphic region of the allele by a small number ofbases, where the small number is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, or 20, or a combination thereof; hybridizingthe pre-circularized probe to purified DNA from the first sample;circularizing the pre-circularized probe; and amplifying some or all ofthe circularized probe. In an embodiment of the present disclosure, thepreferentially enriching the DNA at a plurality of polymorphic locicomprises obtaining a forward probe such that the 3′ end of the forwardprobe is designed to hybridize to the region of DNA immediately upstreamfrom the polymorphic region, and separated from the polymorphic regionby a small number of bases, where the small number is selected from thegroup consisting of 1, 2, 3, 4, 5, 6 to 10, and 11 to 20; obtaining areverse probe such that the 3′ end of the reverse probe is designed tohybridize to the region of DNA immediately downstream from thepolymorphic region, and separated from the polymorphic region by a smallnumber of bases, where the small number is selected from the groupconsisting of 1, 2, 3, 4, 5, 6 to 10, and 11 to 20; hybridizing the twoprobes to DNA in the first sample of DNA; and amplifying the DNA usingthe polymerase chain reaction. In an embodiment of the presentdisclosure, the preferentially enriching the DNA at a plurality ofpolymorphic loci comprises obtaining a set of hybrid capture probes;hybridizing the hybrid capture probes to the DNA in the first sample;and physically separating the hybridized DNA from the first sample ofDNA from the unhybridized DNA from the first sample. In an embodiment ofthe present disclosure, the set of hybrid capture probes are designed tohybridize to a region that is flanking but not crossing the polymorphicallele. In an embodiment of the present disclosure, the set of hybridcapture probes are designed to hybridize to a region that is flankingbut not crossing the polymorphic allele, and wherein the length of theflanking capture probe may be selected from the group consisting of aslow as about 120 bases, as low as about 110 bases, as low as about 100bases, as low as about 90 bases, as low as about 80 bases, as low asabout 70 bases, as low as about 60 bases, as low as about 50 bases, aslow as about 40 bases, as low as about 30 bases, and as low as about 25bases. In an embodiment of the present disclosure, the preferentialenrichment results in average degree of allelic bias between the secondsample and the first sample of a factor selected from the groupconsisting of no more than a factor of 2, no more than a factor of 1.5,no more than a factor of 1.2, no more than a factor of 1.1, no more thana factor of 1.05, no more than a factor of 1.02, no more than a factorof 1.01, no more than a factor of 1.005, no more than a factor of 1.002,no more than a factor of 1.001 and no more than a factor of 1.0001.

In an embodiment of the present disclosure, the set of polymorphicalleles are SNPs. In an embodiment of the present disclosure, the stepof measuring the DNA in the second sample is done by sequencing.

In an embodiment of the present disclosure, the method is executed for aplurality of gestating fetuses, the method further comprisingdetermining the percent of DNA that is fetal in each of the secondfractions; and wherein the step of measuring the DNA in the secondsample is done by sequencing a number of DNA molecules in each of thesecond samples, where more molecules of DNA are sequenced from thosesecond samples that have a smaller fraction of fetal DNA than thosesecond samples that have a larger fraction of fetal DNA. In anembodiment of the present disclosure, the method is executed for aplurality of gestating fetuses, and where the measuring the DNA in thesecond sample is done, for each of the fetuses, by sequencing a fractionof the second sample of DNA to give a first set of measurements, themethod further comprising making a first relative probabilitydetermination for each of the ploidy hypotheses for each of the fetuses,given the first set of DNA measurements; resequencing a second fractionof the second sample from those fetuses where the first relativeprobability determination for each of the ploidy hypotheses indicatesthat a ploidy hypothesis corresponding to an aneuploid fetus has asignificant probability, to give a second set of measurements; making asecond relative probability determination for ploidy hypotheses for thefetuses using the second set of measurements and optionally also thefirst set of measurements; and calling the ploidy states of the fetuseswhose second sample was resequenced by selecting the ploidy statecorresponding to the hypothesis with the greatest probability asdetermined by the second relative probability determination.

In an embodiment of the present disclosure, the step of building a jointdistribution model is done by using data about the probability ofchromosomes crossing over at different crossover locations in achromosome to model dependence between polymorphic alleles on thechromosome. In an embodiment of the present disclosure, the step ofbuilding a joint distribution model and the step of determining therelative probability of each hypothesis are done using a method thatdoes not require the use of a reference chromosome.

In an embodiment of the present disclosure, the step of determining therelative probability of each hypothesis makes use of an estimatedfraction of fetal DNA in the measured sample. In an embodiment of thepresent disclosure, the DNA measurements from the second sample used incalculating allele ratios and determining the relative probability ofeach hypothesis comprise primary genetic data.

In an embodiment of the present disclosure, selecting the ploidy statecorresponding to the hypothesis with the greatest probability is carriedout using maximum likelihood estimates. In an embodiment of the presentdisclosure, the step of calling the ploidy state of the fetus furthercomprises combining the relative probabilities of each of the ploidyhypotheses determined using the joint distribution model and the alleleratios with relative probabilities of each of the ploidy hypotheses thatare calculated using statistical techniques taken from a groupconsisting of a read count analysis, comparing heterozygosity rates, astatistic that is only available when parental genetic information isused, the probability of normalized genotype signals for certain parentcontexts, a statistic that is calculated using an estimated fetalfraction of the first or second mixture, and combinations thereof.

In an embodiment of the present disclosure, a confidence estimate iscalculated for the called ploidy state. In an embodiment of the presentdisclosure, the method further comprises producing a report stating thecalled ploidy state of the fetus. In an embodiment of the presentdisclosure, the method further comprises taking a clinical action basedon the called ploidy state of the fetus, wherein the clinical action isselected from one of terminating the pregnancy or maintaining thepregnancy. In an embodiment of the present disclosure, the method can beperformed at between 4 and 5 weeks gestation; between 5 and 6 weeksgestation; between 6 and 7 weeks gestation; between 7 and 8 weeksgestation; between 8 and 9 weeks gestation; between 9 and 10 weeksgestation; between 10 and 12 weeks gestation; between 12 and 14 weeksgestation; between 14 and 20 weeks gestation; between 20 and 40 weeksgestation; in the first trimester; in the second trimester; or in thethird trimester.

In an embodiment of the present disclosure, a composition is describedcomprising a sample of preferentially enriched DNA, wherein the sampleof preferentially enriched DNA has been preferentially enriched at aplurality of polymorphic loci from a first sample of DNA, wherein thedegree of enrichment is selected from the group consisting of at least10, at least 100, at least 1,000, at least 10,000, at least 100,000, orat least 1,000,000, and wherein the allelic bias between the firstsample and the preferentially enriched sample is, on average, selectedfrom the group consisting of less than 1000%, less than 500%, less than200%, less than 100%, less than 50%, less than 20%, less than 10%, lessthan 5%, less than 2%, less than 1%, less than 0.5%, less than 0.2%,less than 0.1%, less than 0.05%, less than 0.02%, and less than 0.01%.In an embodiment of the present disclosure, a method is to create such asample of preferentially enriched DNA.

In an embodiment of the present disclosure, methods are disclosed fordetermining a fetal aneuploidy by determining the number of copies ofmaternal and fetal target chromosomes, having target sequences in amixture of maternal and fetal genetic material, comprising the steps of(a) obtaining maternal tissue containing both maternal and fetal geneticmaterial; (b) obtaining a mixture of maternal and fetal genetic materialfrom said maternal tissue; (c) distributing the genetic materialobtained in step b) into a plurality of reaction samples, to randomlyprovide individual reaction samples that contain a target sequence froma target chromosome and individual reaction samples that do not containa target sequence from a target chromosome; (d) analyzing the targetsequences of genetic material present or absent in said individualreaction samples to provide a first number of binary resultsrepresenting presence or absence of a presumably euploid fetalchromosome in the reaction samples and a second number of binary resultsrepresenting presence or absence of a possibly aneuploid fetalchromosome in the reaction samples; (e) calculating an expecteddistribution of a number of binary results for a presumably euploidfetal chromosome in the reaction samples using the first number; (f)calculating an expected distribution of a number of binary results for apresumably aneuploid fetal chromosome in the reaction samples using thefirst number and an estimated fraction of fetal DNA found in the mixtureof step (b); and (g) using a maximum likelihood approach to determinewhether the second number indicates the presence of a fetal aneuploidy.

BRIEF DESCRIPTION OF THE DRAWINGS

The presently disclosed embodiments will be further explained withreference to the attached drawings, wherein like structures are referredto by like numerals throughout the several views. The drawings shown arenot necessarily to scale, with emphasis instead generally being placedupon illustrating the principles of the presently disclosed embodiments.

FIG. 1 shows a required number of measurements as a function of childconcentration;

FIG. 2 shows a simulated and estimate child fraction;

FIGS. 3A-3E show hit rates versus child fraction;

FIG. 4 shows hit rates versus confidence;

FIG. 5 shows hit rates versus confidence;

FIGS. 6A and 6B show hit rates versus confidence;

FIGS. 7A and 7B show an estimated versus true dropout rate;

FIGS. 8A-8E show hit rates versus child fraction;

FIG. 9 shows a distribution of reads;

FIG. 10 shows a distribution of reads;

FIG. 11 shows percentiles of the sequence count distributions;

FIG. 12 shows percentiles of the sequence count distributions;

FIGS. 13A and 13B show a number of reads vs. average number of reads;

FIG. 14 shows allele ratios at SNPs versus the number of sequences;

FIG. 15 shows allele ratios at SNPs versus the number of sequences;

FIG. 16 shows estimated allele ratios at SNPs versus the number ofsequences; and

FIGS. 17A and 17B show phred scores.

While the above-identified drawings set forth presently disclosedembodiments, other embodiments are also contemplated, as noted in thediscussion. This disclosure presents illustrative embodiments by way ofrepresentation and not limitation. Numerous other modifications andembodiments can be devised by those skilled in the art which fall withinthe scope and spirit of the principles of the presently disclosedembodiments.

DETAILED DESCRIPTION

In an embodiment, the present disclosure provides ex vivo methods fordetermining the ploidy status of a chromosome in a gestating fetus fromgenotypic data measured from a mixed sample of DNA (i.e., DNA from themother of the fetus, and DNA from the fetus) and from genotypic datameasured from a sample of genetic material from the mother andoptionally also from the father, wherein the determining is done byusing a joint distribution model to create a set of expected alleledistributions for different possible fetal ploidy states given theparental genotypic data, and comparing the expected allelicdistributions to the pattern of measured allelic distributions measuredin the mixed sample, and choosing the ploidy state whose expectedallelic distribution pattern most closely matches the observed allelicdistribution pattern. In an embodiment, the mixed sample is derived frommaternal blood. In an embodiment, the mixed sample of DNA may bepreferentially enriched at a plurality of polymorphic loci. In anembodiment, the preferential enrichment is done in a way that minimizesthe allelic bias. In an embodiment, there is a composition of DNA thathas been preferentially enriched in at a plurality of loci such that theallelic bias is low.

In an embodiment, the present disclosure provides methods fornon-invasive prenatal diagnosis (NPD), specifically, determining theaneuploidy status of a fetus by observing allele distributions at a setof polymorphic alleles in genotypic data measured on DNA mixtures, wherecertain allele distributions are indicative of an aneuploid fetus, whileother allele distributions are indicative of a euploid fetus. In oneembodiment, the genotypic data is measured by sequencing DNA mixturesthat were derived from maternal plasma. In one embodiment, the DNAsample may be preferentially enriched in molecules of DNA thatcorrespond to the set of alleles whose allele distributions are beingcalculated.

In one embodiment, the method involves determining whether thedistribution of observed allele measurements is indicative of a euploidor an aneuploid fetus using a joint distribution model. The use of ajoint distribution model is a significant improvement over methods thatdetermine heterozygosity rates by treating polymorphic lociindependently in that the resultant determinations are of significantlyhigher accuracy. Without being bound by any particular theory, it isbelieved that one reason they are of higher accuracy is that the jointdistribution model takes into account the linkage between SNPs, andlikelihood of crossovers occurring. Another reason it is believed thatthey are of higher accuracy is that they can take into account alleleswhere the total number of reads is low, and the allele ratio methodwould produce disproportionately weighted stochastic noise.

In one embodiment, the method involves determining whether thedistribution of observed allele measurements is indicative of a euploidor an aneuploid fetus using a maximum likelihood technique. The use of amaximum likelihood technique is a significant improvement over methodsthat use single hypothesis rejection technique in that the resultantdeterminations will be made with significantly higher accuracy. Onereason is that single hypothesis rejection techniques set cut offthresholds based on only one measurement distribution rather than two,meaning that the thresholds are usually not optimal. Another reason isthat the maximum likelihood technique allows the optimization of the cutoff threshold for each individual sample instead of determining a cutoff threshold to be used for all samples regardless of the particularcharacteristics of each individual sample. Another reason is that theuse of a maximum likelihood technique allows the calculation of aconfidence for each ploidy call.

In one embodiment, the method involves determining whether thedistribution of observed allele measurements is indicative of a euploidor an aneuploid fetus without comparing the distribution of observedallele measurements on a suspect chromosome to a distribution ofobserved allele measurements on a reference chromosome that is expectedto be disomic. This is a significant improvement over methods thatrequire the use of a reference chromosome to determine whether a suspectchromosome is euploid or aneuploid. One example of where a ploidycalling technique that requires a reference chromosome would make anincorrect call is in the case of a 69XXX trisomic fetus, which would becalled euploid since there is no reference diploid chromosome, while themethod described herein would be able to determine that the fetus wastrisomic.

In one embodiment, the method disclosed herein demonstrates howobserving allele distributions at polymorphic alleles can be used todetermine the ploidy state of a fetus with greater accuracy than methodsin the prior art. In one embodiment, the method involves usingalgorithms that analyze the distribution of alleles found for allelesthat have different parental contexts, and comparing the observed alleledistributions to the expected allele distributions for different ploidystates for the different parental contexts (different parental genotypicpatterns). This is an improvement over methods that do not utilizeallele distribution patterns for alleles from a plurality of differentparental contexts because it allows the use of significantly moregenetic measurement data from a set of sequence data in the ploidydetermination, resulting in a more accurate determination. In oneembodiment, the method involves determining whether the distribution ofobserved allele measurements is indicative of a euploid or an aneuploidfetus using observed allelic distributions measured at loci where themother is heterozygous. This is an improvement over methods that do notuse observed allelic distributions are loci where the mother isheterozygous because it allows the use of about twice as much geneticmeasurement data from a set of sequence data in the ploidydetermination, resulting in a more accurate determination.

In one embodiment, the method disclosed herein uses selective enrichmenttechniques that preserve the allele distributions that are present inthe original sample of DNA. In some embodiments the amplification and/orselective enrichment technique may involve targeted amplification,hybrid capture, or circularizing probes. In some embodiments, methodsfor amplification or selective enrichment may involve using probes wherethe hybridizing region on the probe is separated from the variableregion of the polymorphic allele by a small number of nucleotides. Thisseparation results in lower amounts of allelic bias. This separationresults in lower amounts of allelic bias. This is an improvement overmethods that involve using probes where the hybridizing region on theprobe is designed to hybridize at the base pair directly adjacent to thevariable region of the polymorphic allele. This is an improvement overother methods that involve amplification and/or selective enrichmentmethods that do not preserve the allele distributions that are presentin the original sample of DNA well. Low allelic bias is critical forensuring that the measured genetic data is representative of theoriginal sample in methods that involve either calculating allele ratiosor allele measurement distributions. Since prior methods did not focuson polymorphic regions of the genome, or on the allele distributions, itwas not obvious that techniques that preserved the allele distributionswould result in more accurate ploidy state determinations. Since priormethods did not focus on using allelic distributions to determine ploidystate, it was not obvious that a composition where a plurality of lociwere preferentially enriched with low allelic bias would be particularlyvaluable for determining a ploidy state of a fetus.

The methods described herein are particularly advantageous when used onsamples where a small amount of DNA is available, or where the percentof fetal DNA is low. This is due to the correspondingly higher alleledrop out rate that occurs when only a small amount of DNA is available,or the correspondingly higher fetal allele drop out rate when thepercent of fetal DNA is low. A high allele drop out rate, meaning that alarge percentage of the alleles were not measured for the targetindividual, results in poorly accurate fetal fractions calculations, andpoorly accurate ploidy determinations. Since the method disclosed hereinuses a joint distribution model that takes into account the linkage ininheritance patterns between SNPs, significantly more accurate ploidydeterminations may be made.

It is possible to determine the ploidy state of an individual based onmeasurements when that individual's DNA is mixed with DNA of a relatedindividual. In the case of free floating DNA found in maternal plasma,the DNA from the mother, with known karyotype and known genotype, ismixed with DNA of the fetus, with unknown karyotype and unknowngenotype. It is possible to use the known genotypic information from oneor both parents to predict a plurality of potential compositions of theDNA in the mixed sample for different ploidy states, differentchromosome contributions from each parent to the fetus, and optionally,different fetal DNA fractions in the mixture. Each potential compositionmay be referred to as a hypothesis. The ploidy state of the fetus canthen be determined by looking at the actual measurements, anddetermining which potential compositions are most likely given theobserved data.

Non-Invasive Prenatal Diagnosis (NPD)

The process of non-invasive prenatal diagnosis involves a number ofsteps. Some of the steps may include: (1) obtaining the genetic materialfrom the fetus; (2) enriching the genetic material of the fetus, exvivo; (3) amplifying the genetic material, ex vivo; (4) preferentiallyenriching specific loci in the genetic material, ex vivo; (5) genotypingthe genetic material, ex vivo; and (6) analyzing the genotypic data, ona computer, and ex vivo. Methods to reduce to practice these six andother relevant steps are described herein. At least some of the methodsteps are not directly applied on the body. In an embodiment, thepresent disclosure relates to methods of treatment and diagnosis appliedto tissue and other biological materials isolated and separated from thebody. At least some of the method steps are executed on a computer.

Some embodiments of the present disclosure allow a clinician todetermine the genetic state of a fetus that is gestating in a mother ina non-invasive manner such that the health of the baby is not put atrisk by the collection of the genetic material of the fetus, and thatthe mother is not required to undergo an invasive procedure. Moreover,in certain aspects, the present disclosure allows the fetal geneticstate to be determined with high accuracy, significantly greateraccuracy than, for example, the non-invasive maternal serum analytebased screens, such as the triple test, that are in wide use in prenatalcare.

The accuracy of the methods disclosed herein is a result of aninformatics approach to analysis of the genotype data, as describedherein. Modern technological advances have resulted in the ability tomeasure large amounts of genetic information from a genetic sample usingsuch methods as high throughput sequencing and genotyping arrays. Themethods disclosed herein allow a clinician to take greater advantage ofthe large amounts of data available, and make a more accurate diagnosisof the fetal genetic state. The details of a number of embodiments aregiven below. Different embodiments may involve different combinations ofthe aforementioned steps. Various combinations of the differentembodiments of the different steps may be used interchangeably.

In one embodiment, a blood sample is taken from a pregnant mother, andthe free floating DNA in the plasma of the mother's blood, whichcontains a mixture of both DNA of maternal origin, and DNA of fetalorigin, is used to determine the ploidy status of the fetus. In oneembodiment of the present disclosure, a key step of the method involvespreferential enrichment of those DNA sequences in a mixture of DNA thatcorrespond to polymorphic alleles in a way that the allele ratios and/orallele distributions remain mostly consistent upon enrichment. In oneembodiment of the present disclosure, the method involves sequencing amixture of DNA that contains both DNA of maternal origin, and DNA offetal origin. In one embodiment of the present disclosure, a key step ofthe method involves using measured allele distributions to determine theploidy state of a fetus that is gestating in a mother.

This application makes reference to U.S. Utility application Ser. No.11/603,406, filed Nov. 28, 2006; U.S. Utility application Ser. No.12/076,348, filed Mar. 17, 2008; PCT Utility Application Serial No.PCT/US09/52730, filed Aug. 4, 2009; PCT Utility Application Serial No.PCT/US10/050824, filed Sep. 30, 2010. Some of the vocabulary used inthis filing may have its antecedents in these references. Some of theconcepts described herein may be better understood in light of theconcepts found in these three references.

Screening Maternal Blood Containing Free Floating Fetal DNA

The methods described herein may be used to help determine the genotypeof a child, fetus, or other target individual where the genetic materialof the target is found in the presence of a quantity of other geneticmaterial. In this disclosure, the discussion focuses on determining thegenetic state of a fetus where the fetal DNA is found in maternal blood,but this example is not meant to limit to possible contexts that thismethod may be applied to. In addition, the method may be applicable incases where the amount of target DNA is in any proportion with thenon-target DNA; for example, the target DNA could make up anywherebetween 0.000001 and 99.999999% of the DNA present. In addition, thenon-target DNA does not necessarily need to be from one individual, oreven from a related individual, as long as genetic data from non-targetindividual(s) is known. In one embodiment of the present disclosure, themethod can be used to determine genotypic data of a fetus from maternalblood that contains fetal DNA. It may also be used in a case where thereare multiple fetuses in the uterus of a pregnant woman, or where othercontaminating DNA may be present in the sample, for example from otheralready born siblings.

This technique may make use of the phenomenon of fetal blood cellsgaining access to maternal circulation through the placental villi.Ordinarily, only a very small number of fetal cells enter the maternalcirculation in this fashion (not enough to produce a positiveKleihauer-Betke test for fetal-maternal hemorrhage). The fetal cells canbe sorted out and analyzed by a variety of techniques to look forparticular DNA sequences, but without the risks that these latter twoinvasive procedures inherently have. This technique may also make use ofthe phenomenon of free floating fetal DNA gaining access to maternalcirculation by DNA release following apoptosis of placental tissue wherethe placental tissue in question contains DNA of the same genotype asthe fetus. The free floating DNA found in maternal plasma has been shownto contain fetal DNA in proportions as high as 30-40% fetal DNA.

In one embodiment of the present disclosure, blood may be drawn from apregnant woman. Research has shown that maternal blood may contain asmall amount of free floating DNA from the fetus, in addition to freefloating DNA of maternal origin. In addition, there also may beenucleated fetal blood cells containing DNA of fetal origin, in additionto many blood cells of maternal origin, which typically do not containnuclear DNA. There are many methods know in the art to isolate fetalDNA, or create fractions enriched in fetal DNA. For example,chromatography has been show to create certain fractions that areenriched in fetal DNA.

Once the sample of maternal blood, plasma, or other fluid, drawn in arelatively non-invasive manner, and that contains an amount of fetalDNA, either cellular or free floating, either enriched in its proportionto the maternal DNA, or in its original ratio, is in hand, one maygenotype the DNA found in said sample. The method described herein canbe used to determine genotypic data of the fetus. For example, it can beused to determine the ploidy state at one or more chromosomes, it can beused to determine the identity of one or a set of SNPs, includinginsertions, deletions, and translocations. It can be used to determineone or more haplotypes, including the parent of origin of one or moregenotypic features.

Note that this method will work with any nucleic acids that can be usedfor any genotyping and/or sequencing methods, such as the ILLUMINAINFINIUM ARRAY platform, AFFYMETRIX GENECHIP, ILLUMINA GENOME ANALYZER,or LIFE TECHNOLGIES' SOLID SYSTEM. This includes extracted free-floatingDNA from plasma or amplifications (e.g. whole genome amplification, PCR)of the same; genomic DNA from other cell types (e.g. human lymphocytesfrom whole blood) or amplifications of the same. For preparation of theDNA, any extraction or purification method that generates genomic DNAsuitable for the one of these platforms will work as well. In oneembodiment, storage of the samples may be done in a way that willminimize degradation (e.g. at −20 C or lower).

Parental Support

Some embodiments may be used in combination with the PARENTAL SUPPORT™(PS) method, embodiments of which are described in U.S. application Ser.No. 11/603,406, U.S. application Ser. No. 12/076,348, and internationalapplication PCT/US09/52730, which are incorporated herein by referencein their entirety. PARENTAL SUPPORT™ is an informatics based approachthat can be used to analyze genetic data. In some embodiments, themethods disclosed herein may be considered as part of the PARENTALSUPPORT™ method. In some embodiments, The PARENTAL SUPPORT™ method is acollection of methods that may be used to determine the genetic data,with high accuracy, of one or a small number of cells, specifically todetermine disease-related alleles, other alleles of interest, and/or theploidy state of the cell(s). PARENTAL SUPPORT™ may refer to any of thesemethods. PARENTAL SUPPORT™ is an example of an informatics based method.

The PARENTAL SUPPORT™ method makes use of known parental genetic data,i.e. haplotypic and/or diploid genetic data of the mother and/or thefather, together with the knowledge of the mechanism of meiosis and theimperfect measurement of the target DNA, and possible of one or morerelated individuals, in order to reconstruct, in silico, the genotype ata plurality of alleles, and/or the ploidy state of an embryo or of anytarget cell(s), and the target DNA at the location of key loci with ahigh degree of confidence. The PARENTAL SUPPORT™ method can reconstructnot only single nucleotide polymorphisms (SNPs) that were measuredpoorly, but also insertions and deletions, and SNPs or whole regions ofDNA that were not measured at all. Furthermore, the PARENTAL SUPPORT™method can both measure multiple disease-linked loci as well as screenfor aneuploidy, from a single cell. In some embodiments, the PARENTALSUPPORT™ method may be used to characterize one or more cells fromembryos biopsied during an IVF cycle to determine the genetic conditionof the one or more cells.

The PARENTAL SUPPORT™ method allows the cleaning of noisy genetic data.This may be done by inferring the correct genetic alleles in the targetgenome (embryo) using the genotype of related individuals (parents) as areference. PARENTAL SUPPORT™ may be particularly relevant where only asmall quantity of genetic material is available (e.g. PGD) and wheredirect measurements of the genotypes are inherently noisy due to thelimited amounts of genetic material. The PARENTAL SUPPORT™ method isable to reconstruct highly accurate ordered diploid allele sequences onthe embryo, together with copy number of chromosomes segments, eventhough the conventional, unordered diploid measurements may becharacterized by high rates of allele dropouts, drop-ins, variableamplification biases and other errors. The method may employ both anunderlying genetic model and an underlying model of measurement error.The genetic model may determine both allele probabilities at each SNPand crossover probabilities between SNPs. Allele probabilities may bemodeled at each SNP based on data obtained from the parents and modelcrossover probabilities between SNPs based on data obtained from theHapMap database, as developed by the International HapMap Project. Giventhe proper underlying genetic model and measurement error model, maximuma posteriori (MAP) estimation may be used, with modifications forcomputationally efficiency, to estimate the correct, ordered allelevalues at each SNP in the embryo.

One aspect of the PARENTAL SUPPORT™ technology is a chromosome copynumber calling algorithm that in some embodiments uses parental genotypecontexts. To call the chromosome copy number, the algorithm may use thephenomenon of locus dropout (LDO) combined with distributions ofexpected embryonic genotypes. During whole genome amplification, LDOnecessarily occurs. LDO rate is concordant with the copy number of thegenetic material from which it is derived, i.e., fewer chromosome copiesresult in higher LDO, and vice versa. As such, it follows that loci withcertain contexts of parental genotypes behave in a characteristicfashion in the embryo, related to the probability of alleliccontributions to the embryo. For example, if both parents havehomozygous BB states, then the embryo should never have AB or AA states.In this case, measurements on the A detection channel are expected tohave a distribution determined by background noise and variousinterference signals, but no valid genotypes. Conversely, if bothparents have homozygous AA states, then the embryo should never have ABor BB states, and measurements on the A channel are expected to have themaximum intensity possible given the rate of LDO in a particular wholegenome amplification. When the underlying copy number state of theembryo differs from disomy, loci corresponding to the specific parentalcontexts behave in a predictable fashion, based on the additionalallelic content that is contributed by, or is missing from, one of theparents. This allows the ploidy state at each chromosome, or chromosomesegment, to be determined. The details of one embodiment of this methodare described elsewhere in this disclosure.

The techniques outlined above, in some cases, are able to determine thegenotype of an individual given a very small amount of DNA originatingfrom that individual. This could be the DNA from one or a small numberof cells, or it could be from an even smaller amount of DNA, forexample, DNA found in maternal blood.

In the context of non-invasive prenatal diagnosis, the techniquesdescribed above may not be sufficient to determine the genotype and/orthe ploidy state, or the partial genotype or partial ploidy state(meaning the genetic state of a subset of alleles or chromosomes) of anindividual. This may be especially true when the DNA of the targetindividual is found in maternal blood, and the amount of maternal DNApresent in the sample may be greater than the amount of DNA from thetarget individual. In other cases, the amount of maternal DNA present inthe sample may be in a sufficiently great amount of DNA that it makesthe determination of the genetic state of the target individualdifficult.

DEFINITIONS

-   Single Nucleotide Polymorphism (SNP) refers to a single nucleotide    that may differ between the genomes of two members of the same    species. The usage of the term should not imply any limit on the    frequency with which each variant occurs.-   To Call a SNP refers to the act of making a decision about the true    state of a particular base pair, taking into account the direct and    indirect evidence.-   Sequence refers to a DNA sequence or a genetic sequence. It refers    to the primary, physical structure of the DNA molecule or strand in    an individual. It refers to the sequence of nucleotides found in    that DNA molecule, or the complementary strand to the DNA molecule.-   Locus refers to a particular region of interest on the DNA of an    individual, which may refer to a SNP, the site of a possible    insertion or deletion, or the site of some other relevant genetic    variation. Disease-linked SNPs may also refer to disease-linked    loci.-   Polymorphic Allele, also “Polymorphic Locus,” refers to an allele or    locus where the genotype varies between individuals within a given    species. Some examples of polymorphic alleles include single    nucleotide polymorphisms, short tandem repeats, deletions,    duplications, and inversions.-   Allele refers to the genes that occupy a particular locus.-   To Call an Allele refers to the act of determining the genetic state    at a particular locus of DNA. This may involve calling a SNP, a    plurality of SNPs, or determining whether or not an insertion or    deletion is present at that locus, or determining the number of    insertions that may be present at that locus, or determining whether    some other genetic variant is present at that locus.-   Correct Allele Call refers to an allele call that correctly reflects    the true state of the actual genetic material of an individual.-   To Clean Genetic Data refers to the act of taking imperfect genetic    data and correcting some or all of the errors or fill in missing    data at one or more loci. In the presently disclosed embodiments,    this may involve using the genetic data of related individuals and    the method described herein.-   Genetic Data also “Genotypic Data” refers to the data describing    aspects of the genome of one or more individuals. It may refer to    one or a set of loci, partial or entire sequences, partial or entire    chromosomes, or the entire genome. It may refer to the identity of    one or a plurality of nucleotides; it may refer to a set of    sequential nucleotides, or nucleotides from different locations in    the genome, or a combination thereof. Genotypic data is typically in    silico, however, it is also possible to consider physical    nucleotides in a sequence as chemically encoded genetic data.    Genotypic Data may be said to be “on,” “of,” “at,” “from” or “on”    the individual(s). Genotypic Data may refer to output measurements    from a genotyping platform where those measurements are made on    genetic material.-   Genetic Material also “Genetic Sample” refers to physical matter,    such as tissue or blood, from one or more individuals containing DNA    or RNA-   Imperfect Genetic Data refers to genetic data with any of the    following: allele dropouts, uncertain base pair measurements,    incorrect base pair measurements, missing base pair measurements,    uncertain measurements of insertions or deletions, uncertain    measurements of chromosome segment copy numbers, spurious signals,    missing measurements, other errors, or combinations thereof.-   Noisy Genetic Data, also “Incomplete Genetic Data,” refers to    imperfect genetic data.-   Uncleaned Genetic Data, also “Crude Genetic Data,” refers to genetic    data as measured, that is, where no method has been used to correct    for the presence of noise or errors in the raw genetic data.-   Confidence refers to the statistical likelihood that the called SNP,    allele, set of alleles, ploidy call, or determined number of    chromosome segment copies correctly represents the real genetic    state of the individual.-   Ploidy Calling, also “Chromosome Copy Number Calling,” or “Copy    Number Calling” (CNC), refers to the act of determining the quantity    and chromosomal identity of one or more chromosomes present in a    cell.-   Aneuploidy refers to the state where the wrong number of chromosomes    are present in a cell. In the case of a somatic human cell it refers    to the case where a cell does not contain 22 pairs of autosomal    chromosomes and one pair of sex chromosomes. In the case of a human    gamete, it refers to the case where a cell does not contain one of    each of the 23 chromosomes. In the case of a single chromosome, it    refers to the case where more or less than two homologous but    non-identical chromosomes are present, and where each of the two    chromosomes originate from a different parent.-   Ploidy State refers to the quantity and chromosomal identity of one    or more chromosomes in a cell.-   Chromosomal Identity refers to the referent chromosome number.    Normal humans have 22 types of numbered autosomal chromosomes, and    two types of sex chromosomes. It may also refer to the parental    origin of the chromosome. It may also refer to a specific chromosome    inherited from the parent. It may also refer to other identifying    features of a chromosome.-   The State of the Genetic Material or simply “Genetic State” refers    to the identity of a set of SNPs on the DNA, to the phased    haplotypes of the genetic material, and to the sequence of the DNA,    including insertions, deletions, repeats and mutations. It may also    refer to the ploidy state of one or more chromosomes, chromosomal    segments, or set of chromosomal segments.-   Allelic Data refers to a set of genotypic data concerning a set of    one or more alleles. It may refer to the phased, haplotypic data. It    may refer to SNP identities, and it may refer to the sequence data    of the DNA, including insertions, deletions, repeats and mutations.    It may include the parental origin of each allele.-   Allelic State refers to the actual state of the genes in a set of    one or more alleles. It may refer to the actual state of the genes    described by the allelic data.-   Allelic Distribution refers to the distribution of the set of    alleles observed at a set of loci. An allelic distribution for one    locus is an allele ratio.-   Allelic Distribution Pattern refers to a set of different allele    distributions for different parental contexts. Certain allelic    distribution patterns may be indicative of certain ploidy states.-   Allelic Bias refers to the degree to which the measured ratio of    alleles at a heterozygous locus is different to the ratio that was    present in the original sample of DNA. The degree of allelic bias at    a particular locus is equal to the observed allelic ratio at that    locus, as measured, divided by the ratio of alleles in the original    DNA sample at that locus. Allelic bias may be defined to be greater    than one, such that if the calculation of the degree of allelic bias    returns a value, x, that is less than 1, then the degree of allelic    bias may be restated as 1/x.-   Matched Copy Error, also “Matching Chromosome Aneuploidy” (MCA),    refers to a state of aneuploidy where one cell contains two    identical or nearly identical chromosomes. This type of aneuploidy    may arise during the formation of the gametes in mitosis, and may be    referred to as a mitotic non-disjunction error. Matching trisomy may    refer to the case where three copies of a given chromosome are    present in an individual and two of the copies are identical.-   Unmatched Copy Error, also “Unique Chromosome Aneuploidy” (UCA),    refers to a state of aneuploidy where one cell contains two    chromosomes that are from the same parent, and that may be    homologous but not identical. This type of aneuploidy may arise    during meiosis, and may be referred to as a meiotic error.    Unmatching trisomy may refer to the case where three copies of a    given chromosome are present in an individual and two of the copies    are from the same parent, and are homologous, but are not identical.-   Homologous Chromosomes refers to chromosomes that contain the same    set of genes that normally pair up during meiosis.-   Identical Chromosomes refers to chromosomes that contain the same    set of genes, and for each gene they have the same set of alleles    that are identical, or nearly identical.-   Allele Drop Out (ADO) refers to the situation where one of the base    pairs in a set of base pairs from homologous chromosomes at a given    allele is not detected.-   Locus Drop Out (LDO) refers to the situation where both base pairs    in a set of base pairs from homologous chromosomes at a given allele    are not detected.-   Homozygous refers to having similar alleles as corresponding    chromosomal loci.-   Heterozygous refers to having dissimilar alleles as corresponding    chromosomal loci.-   Heterozygosity Rate refers to the rate of individuals in the    population having heterozygous alleles at a given locus. The    heterozygosity rate may also refer to the expected or measured ratio    of alleles, at a given locus in an individual, or a sample of DNA.-   Highly Informative Single Nucleotide Polymorphism (HISNP) refers to    a SNP where the fetus has an allele that is not present in the    mother's genotype.-   Chromosomal Region refers to a segment of a chromosome, or a full    chromosome.-   Segment of a Chromosome refers to a section of a chromosome that can    range in size from one base pair to the entire chromosome.-   Chromosome refers to either a full chromosome, or also a segment or    section of a chromosome.-   Copies refers to the number of copies of a chromosome segment, to    identical copies, or to non-identical, homologous copies of a    chromosome segment wherein the different copies of the chromosome    segment contain a substantially similar set of loci, and where one    or more of the alleles are different. Note that in some cases of    aneuploidy, such as the M2 copy error, it is possible to have some    copies of the given chromosome segment that are identical as well as    some copies of the same chromosome segment that are not identical.-   Haplotype refers to a combination of alleles at multiple loci that    are transmitted together on the same chromosome. Haplotype may refer    to as few as two loci or to an entire chromosome depending on the    number of recombination events that have occurred between a given    set of loci. Haplotype can also refer to a set of single nucleotide    polymorphisms (SNPs) on a single chromatid that are statistically    associated.-   Haplotypic Data, also “Phased Data” or “Ordered Genetic Data,”    refers to data from a single chromosome in a diploid or polyploid    genome, i.e., either the segregated maternal or paternal copy of a    chromosome in a diploid genome.-   Phasing refers to the act of determining the haplotypic genetic data    of an individual given unordered, diploid (or polyploidy) genetic    data. It may refer to the act of determining which of two genes at    an allele, for a set of alleles found on one chromosome, are    associated with each of the two homologous chromosomes in an    individual.-   Phased Data refers to genetic data where the haplotype has been    determined.-   Unordered Genetic Data refers to pooled data derived from    measurements on two or more chromosomes in a diploid or polyploid    genome, e.g., both the maternal and paternal copies of a particular    chromosome in a diploid genome.-   Hypothesis refers to a set of possible ploidy states at a given set    of chromosomes, or a set of possible allelic states at a given set    of loci. The set of possibilities may contain one or more elements.-   Copy Number Hypothesis, also “Ploidy State Hypothesis,” refers to a    hypothesis concerning the number of copies of a particular    chromosome in an individual. It may also refer to a hypothesis    concerning the identity of each of the chromosomes, including the    parent of origin of each chromosome, and which of the parent's two    chromosomes are present in the individual. It may also refer to a    hypothesis concerning which chromosomes, or chromosome segments, if    any, from a related individual correspond genetically to a given    chromosome from an individual.-   Allelic Hypothesis refers to a possible allelic state for a given    set of alleles. A set of allelic hypotheses may refer to a set of    hypotheses that describe, together, all of the possible allelic    states in the set of alleles. It may also refer to a hypothesis    concerning which chromosomes, or chromosome segments, if any, from a    related individual correspond genetically to a given chromosome from    an individual.-   Target Individual refers to the individual whose genetic data is    being determined. In one context, only a limited amount of DNA is    available from the target individual. In one context, the target    individual is a fetus. In some embodiments, there may be more than    one target individual. In some embodiments, each fetus that    originated from a pair of parents may be considered to be target    individuals.-   Related Individual refers to any individual who is genetically    related to, and thus shares haplotype blocks with, the target    individual. In one context, the related individual may be a genetic    parent of the target individual, or any genetic material derived    from a parent, such as a sperm, a polar body, an embryo, a fetus, or    a child. It may also refer to a sibling, parent or a grandparent.-   Sibling refers to any individual whose parents are the same as the    individual in question. In some embodiments, it may refer to a born    child, an embryo, or a fetus, or one or more cells originating from    a born child, an embryo, or a fetus. A sibling may also refer to a    haploid individual that originates from one of the parents, such as    a sperm, a polar body, or any other set of haplotypic genetic    matter. An individual may be considered to be a sibling of itself.-   Fetal refers to “of the fetus,” but it also may refer to “of the    placenta”. In a pregnant woman, some portion of the placenta is    genetically similar to the fetus, and the free floating fetal DNA    found in maternal blood may have originated from the portion of the    placenta with a genotype that matches the fetus. Note that the    genetic information in half of the chromosomes in a fetus were    inherited from the mother of the fetus. In some embodiments, the DNA    from these maternally inherited chromosomes that came from a fetal    cell are considered to be “of fetal origin,” not “of maternal    origin.”-   DNA of Fetal Origin refers to DNA that was originally part of a cell    whose genotype was essentially equivalent to that of the fetus.-   DNA of Maternal Origin refers to DNA that was originally part of a    cell whose genotype was essentially equivalent to that of the    mother.-   Child is used interchangeably with the terms embryo, blastomere, and    fetus. Note that in the presently disclosed embodiments, the    concepts described apply equally well to individuals who are a born    child, a fetus, an embryo or a set of cells therefrom. The use of    the term child may simply be meant to connote that the individual    referred to as the child is the genetic offspring of the parents.-   Parent refers to the genetic mother or father of an individual. An    individual typically has two parents, a mother and a father. A    parent may be considered to be an individual.-   Parental Context refers to the genetic state of a given SNP, on each    of the two relevant chromosomes for each of the two parents of the    target.-   Develop As Desired, also “Develop Normally,” refers to a viable    embryo implanting in a uterus and resulting in a pregnancy. It may    also refer to the pregnancy continuing and resulting in a live    birth. It may also refer to the born child being free of chromosomal    abnormalities. It may also refer to the born child being free of    other undesired genetic conditions such as disease-linked genes. The    term “develop as desired” encompasses anything that may be desired    by parents or healthcare facilitators. In some cases, “develop as    desired” may refer to an unviable or viable embryo that is useful    for medical research or other purposes.-   Insertion Into a Uterus refers to the process of transferring an    embryo into the uterine cavity in the context of in vitro    fertilization.-   Clinical Decision refers to any decision to take or not take an    action that has an outcome that affects the health or survival of an    individual. In the context of prenatal diagnosis, a clinical    decision refers to a decision to abort or not abort a fetus. A    clinical decision may also refer to a decision to conduct further    testing, to take actions to mitigate an undesirable phenotype, or to    take actions to prepare for the birth of a child with abnormalities.-   Platform Response refers to the mathematical characterization of the    input/output characteristics of a genetic measurement platform, and    may be used as a measure of the statistically predictable    measurement differences. The platform response may concern the    mathematical characterization of expected possible error rates in a    set of data measured from a genotyping platform.-   Informatics Based Method refers to a method designed to determine    the ploidy state at one or more chromosomes or the allelic state at    one or more alleles by statistically inferring the most likely    state, rather than by directly physically measuring the state. In    one embodiment of the present disclosure, the informatics based    technique may be one disclosed in this patent. In one embodiment of    the present disclosure it may be PARENTAL SUPPORT™.-   Primary Genetic Data refers to the analog intensity signals that are    output by a genotyping platform. In the context of SNP arrays,    primary genetic data refers to the intensity signals before any    genotype calling has been done. In the context of sequencing,    primary genetic data refers to the analog measurements, analogous to    the chromatogram, that comes off the sequencer before the identity    of any base pairs have been determined, and before the sequence has    been mapped to the genome.-   Secondary Genetic Data refers to processed genetic data that are    output by a genotyping platform. In the context of a SNP array, the    secondary genetic data refers to the allele calls made by software    associated with the SNP array reader, wherein the software has made    a call whether a given allele is present or not present in the    sample. In the context of sequencing, the secondary genetic data    refers to the base pair identities of the sequences have been    determined, and possibly also the sequences have been mapped to the    genome.-   Non-Invasive Prenatal Diagnosis (NPD), or also “Non-Invasive    Prenatal Screening” (NPS), refers to a method of determining the    genetic state of a fetus that is gestating in a mother using genetic    material found in the mother's blood, where the genetic material is    obtained by drawing the mother's intravenous blood.-   Preferential Enrichment of DNA that corresponds to a locus, or    preferential enrichment of DNA at a locus, refers to any method that    results in the percentage of molecules of DNA in a post-enrichment    DNA mixture that correspond to the locus being higher than the    percentage of molecules of DNA in the pre-enrichment DNA mixture    that correspond to the locus. The method may involve selective    amplification of DNA molecules that correspond to a locus. The    method may involve removing DNA molecules that do not correspond to    the locus. The method may involve a combination of methods. The    degree of enrichment is defined as the percentage of molecules of    DNA in the post-enrichment mixture that correspond to the locus    divided by the percentage of molecules of DNA in the pre-enrichment    mixture that correspond to the locus. Preferential enrichment may be    carried out at a plurality of loci. In some embodiments of the    present disclosure, the degree of enrichment is greater than 20. In    some embodiments of the present disclosure, the degree of enrichment    is greater than 200. When preferential enrichment is carried out at    a plurality of loci, the degree of enrichment may refer to the    average degree of enrichment of all of the loci.-   Amplification refers to a method that increases the number of copies    of a molecule of DNA.-   Selective Amplification refers to a method that increases the number    of copies of a particular molecule of DNA, or molecules of DNA that    correspond to a particular region of DNA. It may also refer to a    method that increases the number of copies of a particular targeted    molecule of DNA, or targeted region of DNA more than it increases    non-targeted molecules or regions of DNA. Selective amplification    may be a method of preferential enrichment.-   Targeting refers to a method used to preferentially enrich those    molecules of DNA that correspond to a set of loci, in a mixture of    DNA.-   Joint Distribution Model refers to a model that defines the    probability of events defined in terms of multiple random variables,    given a plurality of random variables defined on the same    probability space, where the probabilities of the variable are    linked.

Different Implementations of the Presently Disclosed Embodiments

Any of the embodiments disclosed herein may be implemented in digitalelectronic circuitry, integrated circuitry, specially designed ASICs(application-specific integrated circuits), computer hardware, firmware,software, or in combinations thereof. Apparatus of the presentlydisclosed embodiments can be implemented in a computer program producttangibly embodied in a machine-readable storage device for execution bya programmable processor; and method steps of the presently disclosedembodiments can be performed by a programmable processor executing aprogram of instructions to perform functions of the presently disclosedembodiments by operating on input data and generating output. Thepresently disclosed embodiments can be implemented advantageously in oneor more computer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichmay be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device. Eachcomputer program can be implemented in a high-level procedural orobject-oriented programming language, or in assembly or machine languageif desired; and in any case, the language can be a compiled orinterpreted language. A computer program may be deployed in any form,including as a stand-alone program, or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program may be deployed to be executed or interpreted on onecomputer or on multiple computers at one site, or distributed acrossmultiple sites and interconnected by a communication network.

Computer readable storage media, as used herein, refers to physical ortangible storage (as opposed to signals) and includes without limitationvolatile and non-volatile, removable and non-removable media implementedin any method or technology for the tangible storage of information suchas computer-readable instructions, data structures, program modules orother data. Computer readable storage media includes, but is not limitedto, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memorytechnology, CD-ROM, DVD, or other optical storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other physical or material medium which can be used to tangiblystore the desired information or data or instructions and which can beaccessed by a computer or processor.

Any of the methods described herein may include the output of data in aphysical format, such as on a computer screen, or on a paper printout.In explanations of any embodiments elsewhere in this document, it shouldbe understood that the described methods may be combined with the outputof the actionable data in a format that can be acted upon by aphysician. In addition, the described methods may be combined with theactual execution of a clinical decision that results in a clinicaltreatment, or the execution of a clinical decision to make no action.Some of the embodiments described in the document for determininggenetic data pertaining to a target individual may be combined with thedecision to select one or more embryos for transfer in the context ofIVF, optionally combined with the process of transferring the embryo tothe womb of the prospective mother. Some of the embodiments described inthe document for determining genetic data pertaining to a targetindividual may be combined with the notification of a potentialchromosomal abnormality, or lack thereof, with a medical professional,optionally combined with the decision to abort, or to not abort, a fetusin the context of prenatal diagnosis. Some of the embodiments describedherein may be combined with the output of the actionable data, and theexecution of a clinical decision that results in a clinical treatment,or the execution of a clinical decision to make no action.

Hypotheses

A hypothesis may refer to a possible genetic state. It may refer to apossible ploidy state. It may refer to a possible allelic state. A setof hypotheses refers to a set of possible genetic states. In someembodiments, a set of hypotheses may be designed such that onehypothesis from the set will correspond to the actual genetic state ofany given individual. In some embodiments, a set of hypotheses may bedesigned such that every possible genetic state may be described by atleast one hypothesis from the set. In some embodiments of the presentdisclosure, one aspect of the method is to determine which hypothesiscorresponds to the actual genetic state of the individual in question.

In another embodiment of the present disclosure, one step involvescreating a hypothesis. In some embodiments it may be a copy numberhypothesis. In some embodiments it may involve a hypothesis concerningwhich segments of a chromosome from each of the related individualscorrespond genetically to which segments, if any, of the other relatedindividuals. Creating a hypothesis may refer to the act of setting thelimits of the variables such that the entire set of possible geneticstates that are under consideration are encompassed by those variables.

A “copy number hypothesis,” also called a “ploidy hypothesis,” or a“ploidy state hypothesis,” may refer to a hypothesis concerning apossible ploidy state for a given chromosome, or section of achromosome, in the target individual. It may also refer to the ploidystate at more than one of the chromosomes in the individual. A set ofcopy number hypotheses may refer to a set of hypotheses where eachhypothesis corresponds to a different possible ploidy state in anindividual. A set of hypotheses concern to a set of possible ploidystates, a set of possible parental haplotype contributions, a set ofpossible fetal DNA percentages in the mixed sample, or combinationsthereof.

A normal individual contains one of each chromosome from each parent.However, due to errors in meiosis and mitosis, it is possible for anindividual to have 0, 1, 2, or more of a given chromosome from eachparent. In practice, it is rare to see more that two of a givenchromosomes from a parent. In this disclosure, the embodiments onlyconsider the possible hypotheses where 0, 1, or 2 copies of a givenchromosome come from a parent. In some embodiments, for a givenchromosome, there are nine possible hypotheses: the three possiblehypothesis concerning 0, 1, or 2 chromosomes of maternal origin,multiplied by the three possible hypotheses concerning 0, 1, or 2chromosomes of paternal origin. Let (m,f) refer to the hypothesis wherem is the number of a given chromosome inherited from the mother, and fis the number of a given chromosome inherited from the father.Therefore, the nine hypotheses are (0,0), (0,1), (0,2), (1,0), (1,1),(1,2), (2,0), (2,1), and (2,2). These may also be written as H₀₀, H₀₁,H₀₂, H₁₀, H₁₂, H₂₀, H₂₁, and H₂₂. The different hypotheses correspond todifferent ploidy states. For example, (1,1) refers to a normal disomicchromosome; (2,1) refers to a maternal trisomy, and (0,1) refers to apaternal monosomy. In some embodiments, the case where two chromosomesare inherited from one parent and one chromosome is inherited from theother parent may be further differentiated into two cases: one where thetwo chromosomes are identical (matched copy error), and one where thetwo chromosomes are homologous but not identical (unmatched copy error).In these embodiments, there are sixteen possible hypotheses. It shouldbe understood that it is possible to use other sets of hypotheses, and adifferent number of hypotheses.

In some embodiments of the present disclosure, the ploidy hypothesis mayrefer to a hypothesis concerning which chromosome from other relatedindividuals correspond to a chromosome found in the target individual'sgenome. In some embodiments, a key to the method is the fact thatrelated individuals can be expected to share haplotype blocks, and usingmeasured genetic data from related individuals, along with a knowledgeof which haplotype blocks match between the target individual and therelated individual, it is possible to infer the correct genetic data fora target individual with higher confidence than using the targetindividual's genetic measurements alone. As such, in some embodiments,the ploidy hypothesis may concern not only the number of chromosomes,but also which chromosomes in related individuals are identical, ornearly identical, with one or more chromosomes in the target individual.

An allelic hypothesis, or an “allelic state hypothesis” may refer to ahypothesis concerning a possible allelic state of a set of alleles. Insome embodiments, a key to this method is, as described above, relatedindividuals may share haplotype blocks, which may help thereconstruction of genetic data that was not perfectly measured. Anallelic hypothesis may also refer to a hypothesis concerning whichchromosomes, or chromosome segments, if any, from a related individualcorrespond genetically to a given chromosome from an individual. Thetheory of meiosis tells us that each chromosome in an individual isinherited from one of the two parents, and this is a nearly identicalcopy of a parental chromosome. Therefore, if the haplotypes of theparents are known, that is, the phased genotype of the parents, then thegenotype of the child may be inferred as well. (The term child, here, ismeant to include any individual formed from two gametes, one from themother and one from the father.) In one embodiment of the presentdisclosure, the allelic hypothesis describes a possible allelic state,at a set of alleles, including the haplotypes, as well as whichchromosomes from related individuals may match the chromosome(s) whichcontain the set of alleles.

Once the set of hypotheses have been defined, when the algorithmsoperate on the input genetic data, they may output a determinedstatistical probability for each of the hypotheses under consideration.The probabilities of the various hypotheses may be determined bymathematically calculating, for each of the various hypotheses, thevalue that the probability equals, as stated by one or more of theexpert techniques, algorithms, and/or methods described elsewhere inthis disclosure, using the relevant genetic data as input.

Once the probabilities of the different hypotheses are estimated, asdetermined by a plurality of techniques, they may be combined. This mayentail, for each hypothesis, multiplying the probabilities as determinedby each technique. The product of the probabilities of the hypothesesmay be normalized. Note that one ploidy hypothesis refers to onepossible ploidy state for a chromosome.

The process of “combining probabilities,” also called “combininghypotheses,” or combining the results of expert techniques, is a conceptthat should be familiar to one skilled in the art of linear algebra. Onepossible way to combine probabilities is as follows: When an experttechnique is used to evaluate a set of hypotheses given a set of geneticdata, the output of the method is a set of probabilities that areassociated, in a one-to-one fashion, with each hypothesis in the set ofhypotheses. When a set of probabilities that were determined by a firstexpert technique, each of which are associated with one of thehypotheses in the set, are combined with a set of probabilities thatwere determined by a second expert technique, each of which areassociated with the same set of hypotheses, then the two sets ofprobabilities are multiplied. This means that, for each hypothesis inthe set, the two probabilities that are associated with that hypothesis,as determined by the two expert methods, are multiplied together, andthe corresponding product is the output probability. This process may beexpanded to any number of expert techniques. If only one experttechnique is used, then the output probabilities are the same as theinput probabilities. If more than two expert techniques are used, thenthe relevant probabilities may be multiplied at the same time. Theproducts may be normalized so that the probabilities of the hypothesesin the set of hypotheses sum to 100%.

In some embodiments, if the combined probabilities for a givenhypothesis are greater than the combined probabilities for any of theother hypotheses, then it may be considered that that hypothesis isdetermined to be the most likely. In some embodiments, a hypothesis maybe determined to be the most likely, and the ploidy state, or othergenetic state, may be called if the normalized probability is greaterthan a threshold. In one embodiment, this may mean that the number andidentity of the chromosomes that are associated with that hypothesis maybe called as the ploidy state. In one embodiment, this may mean that theidentity of the alleles that are associated with that hypothesis may becalled as the allelic state. In some embodiments, the threshold may bebetween about 50% and about 80%. In some embodiments the threshold maybe between about 80% and about 90%. In some embodiments the thresholdmay be between about 90% and about 95%. In some embodiments thethreshold may be between about 95% and about 99%. In some embodimentsthe threshold may be between about 99% and about 99.9%. In someembodiments the threshold may be above about 99.9%.

Parental Contexts

The parental context may refer to the genetic state of a given SNP, oneach of the two relevant chromosomes for each of the two parents of thetarget. Note that in one embodiment, the parental context does not referto the allelic state of the target, rather, it refers to the allelicstate of the parents. The parental context for a given SNP may consistof four base pairs, two paternal and two maternal; they may be the sameor different from one another. It is typically written as “m₁m₂|f₁f₂,”where m₁ and m₂ are the genetic state of the given SNP on the twomaternal chromosomes, and f₁ and f₂ are the genetic state of the givenSNP on the two paternal chromosomes. In some embodiments, the parentalcontext may be written as “f₁f₂|m₁m₂.” Note that subscripts “1” and “2”refer to the genotype, at the given allele, of the first and secondchromosome; also note that the choice of which chromosome is labeled “1”and which is labeled “2” is arbitrary.

Note that in this disclosure, A and B are often used to genericallyrepresent base pair identities; A or B could equally well represent C(cytosine), G (guanine), A (adenine) or T (thymine). For example, if, ata given allele, the mother's genotype was T on one chromosome, and G onthe homologous chromosome, and the father's genotype at that allele is Gon both of the homologous chromosomes, one may say that the targetindividual's allele has the parental context of AB|BB; it could also besaid that the allele has the parental context of AB|AA. Note that, intheory, any of the four possible nucleotides could occur at a givenallele, and thus it is possible, for example, for the mother to have agenotype of AT, and the father to have a genotype of GC at a givenallele. However, empirical data indicate that in most cases only two ofthe four possible base pairs are observed at a given allele. In thisdisclosure the discussion assumes that only two possible base pairs willbe observed at a given allele, although the embodiments disclosed hereincould be modified to take into account the cases where this assumptiondoes not hold.

A “parental context” may refer to a set or subset of target SNPs thathave the same parental context. For example, if one were to measure 1000alleles on a given chromosome on a target individual, then the contextAA|BB could refer to the set of all alleles in the group of 1,000alleles where the genotype of the mother of the target was homozygous,and the genotype of the father of the target is homozygous, but wherethe maternal genotype and the paternal genotype are dissimilar at thatlocus. If the parental data is not phased, and thus AB=BA, then thereare nine possible parental contexts: AA|AA, AA|AB, AA|BB, AB|AA, AB|AB,AB|BB, BB|AA, BB|AB, and BB|BB. If the parental data is phased, and thusAB≠BA, then there are sixteen different possible parental contexts:AA|AA, AA|AB, AA|BA, AA|BB, AB|AA, AB|AB, AB|BA, AB|BB, BA|AA, BA|AB,BA|BA, BA|BB, BB|AA, BB|AB, BB|BA, and BB|BB. Every SNP allele on achromosome, excluding some SNPs on the sex chromosomes, has one of theseparental contexts. The set of SNPs wherein the parental context for oneparent is heterozygous may be referred to as the heterozygous context.

Use of Parental Contexts in Sequencing

Non-invasive prenatal diagnosis is an important technique that can beused to determine the genetic state of a fetus from genetic materialthat is obtained in a non-invasive manner, for example from a blood drawon the pregnant mother. The blood could be separated and the plasmaisolated, and size selection could also be used to isolate the DNA ofthe appropriate length. This isolated DNA can then be measured by anumber of means, such as by hybridizing to a genotyping array andmeasuring the fluorescence, or by sequencing on a high throughputsequencer.

When sequencing is used for ploidy calling of a fetus in the context ofnon-invasive prenatal diagnosis, there are a number of ways to use thesequence data. The most common way one could use the sequence data is tosimply count the number of reads that map to a given chromosome. Forexample, imagine if you are trying to figure out the ploidy state ofchromosome 21 on the fetus. Further imagine that the DNA in the sampleis comprised of 10% DNA of fetal origin, and 90% DNA of maternal origin.In this case, you could look at the average number of reads on achromosome which can be expected to be disomic, for example chromosome3, and compare that to the number of read on chromosome 21, where thereads are adjusted for the number of base pairs on that chromosome thatare part of a unique sequence. If the fetus were euploid, one wouldexpect the amount of DNA per unit of genome to be about equal at alllocations (subject to stochastic variations). On the other hand, if thefetus were trisomic at chromosome 21, then one would expect there to bemore slightly more DNA per genetic unit from chromosome 21 than theother locations on the genome. Specifically one would expect there to beabout 5% more DNA from chromosome 21 in the mixture. When sequencing isused to measure the DNA, one would expect about 5% more uniquelymappable reads from chromosome 21 per unique segment than from the otherchromosomes. One could use the observation of an amount of DNA from aparticular chromosome that is higher than a certain threshold, whenadjusted for the number of sequences that are uniquely mappable to thatchromosome, as the basis for an aneuploidy diagnosis. Another methodthat may be used to detect aneuploidy is similar to that above, exceptthat parental contexts could be taken into account.

When considering which alleles to target, one may consider thelikelihood that some parental contexts are likely to be more informativethan others. For example, AA|BB and the symmetric context BB|AA are themost informative contexts, because the fetus is known to carry an allelethat is different from the mother. For reasons of symmetry, both AA|BBand BB|AA contexts may be referred to as AA|BB. Another set ofinformative parental contexts are AA|AB and BB|AB, because in thesecases the fetus has a 50% chance of carrying an allele that the motherdoes not have. For reasons of symmetry, both AA|AB and BB|AB contextsmay be referred to as AA|AB. A third set of informative parentalcontexts are AB|AA and AB|BB, because in these cases the fetus iscarrying a known paternal allele, and that allele is also present in thematernal genome. For reasons of symmetry, both AB|AA and AB|BB contextsmay be referred to as AB|AA. A fourth parental context is AB|AB wherethe fetus has an unknown allelic state, and whatever the allelic state,it is one in which the mother has the same alleles. The fifth parentalcontext is AA|AA, where the mother and father are heterozygous.

Sample Preparation

In some embodiments, the method may involve amplifying DNA. One methodof amplifying DNA is polymerase chain reaction (PCR). One method ofamplifying DNA is whole genome amplification (WGA). There are threemajor methods available for WGA: ligation-mediated PCR (LM-PCR),degenerate oligonucleotide primer PCR (DOP-PCR), and multipledisplacement amplification (MDA). In LM-PCR, short DNA sequences calledadapters are ligated to blunt ends of DNA. These adapters containuniversal amplification sequences, which are used to amplify the DNA byPCR. In DOP-PCR, random primers that also contain universalamplification sequences are used in a first round of annealing and PCR.Then, a second round of PCR is used to amplify the sequences furtherwith the universal primer sequences. MDA uses the phi-29 polymerase,which is a highly processive and non-specific enzyme that replicates DNAand has been used for single-cell analysis. The major limitations toamplification of material from a single cell are (1) necessity of usingextremely dilute DNA concentrations or extremely small volume ofreaction mixture, and (2) difficulty of reliably dissociating DNA fromproteins across the whole genome. Regardless, single-cell whole genomeamplification has been used successfully for a variety of applicationsfor a number of years. There are other method of amplifying DNA from asample of DNA.

There are numerous difficulties in using DNA amplification in thesecontexts. Amplification of single-cell DNA (or DNA from a small numberof cells, or from smaller amounts of DNA) by PCR can fail completely, asreported in 5-10% of the cases. This is often due to contamination ofthe DNA, the loss of the cell, its DNA, or accessibility of the DNAduring the PCR reaction. Other sources of error that may arise inmeasuring the fetal DNA by amplification and microarray analysis includetranscription errors introduced by the DNA polymerase where a particularnucleotide is incorrectly copied during PCR, and microarray readingerrors due to imperfect hybridization on the array. The biggest problem,however, remains allele drop-out (ADO) defined as the failure to amplifyone of the two alleles in a heterozygous cell. ADO can affect up to morethan 40% of amplifications and has already caused PGD misdiagnoses. ADObecomes a health issue especially in the case of a dominant disease,where the failure to amplify can lead to implantation of an affectedembryo. The need for more than one set of primers per each marker (inheterozygotes) complicate the PCR process. Therefore, more reliable PCRassays are being developed based on understanding the ADO origin.Reaction conditions for single-cell amplifications are under study. Theamplicon size, the amount of DNA degradation, freezing and thawing, andthe PCR program and conditions can each influence the rate of ADO.

Several techniques are in development to measure multiple SNPs on theDNA of a small number of cells, a single cell (for example, ablastomere), a small number of chromosomes, or from fragments of DNAsuch as those fragments found in plasma. There are techniques that usePolymerase Chain Reaction (PCR), followed by microarray genotypinganalysis. Some PCR-based techniques include whole genome amplification(WGA) techniques such as multiple displacement amplification (MDA), andMolecular Inversion Probes (MIPS) that perform genotyping using multipletagged oligonucleotides that may then be amplified using PCR with asingle pair of primers.

Targeted Sequencing

The use of a method to target certain alleles followed by sequencing aspart of a method for allele calling or ploidy calling may confer anumber of unexpected advantages. Some methods by which DNA may betargeted, or selectively enriched, include using circularizing probes,linked inverted probes (LIPs), capture by hybridization methods such asSURE SELECT, and targeted PCR amplification strategies.

Some embodiments of the present disclosure involve the use of “LinkedInverted Probes” (LIPs), which have been previously described in theliterature. LIPs is a generic term meant to encompass technologies thatinvolve the creation of a circular molecule of DNA, where the probes aredesigned to hybridize to targeted region of DNA on either side of atargeted allele, such that addition of appropriate polymerases and/orligases, and the appropriate conditions, buffers and other reagents,will complete the complementary, inverted region of DNA across thetargeted allele to create a circular loop of DNA that captures theinformation found in the targeted allele. LIPs may also be calledpre-circularized probes, pre-circularizing probes, or the circularizingprobes. The LIPs probe may be a linear DNA molecule between 50 and 500nucleotides in length, and in a preferred embodiment between 70 and 100nucleotides in length; in some embodiments, it may be longer or shorterthan described herein. Others embodiments of the present disclosureinvolve different incarnations, of the LIPs technology, such as PadlockProbes and Molecular Inversion Probes (MIPs).

In some embodiments of the present disclosure described herein, themethod involves measuring genetic data for use with an informatics basedmethod, such as PARENTAL SUPPORT™ (PS). PARENTAL SUPPORT™ is aninformatics based approach to manipulating genetic data, aspects ofwhich are described herein. The ultimate outcome of some of theembodiments is the actionable genetic data of an embryo or a fetus. Thealgorithms behind the PS method take the measured genetic data of thetarget individual, often an embryo or fetus, and the measured geneticdata from related individuals, and are able to increase the accuracywith which the genetic state of the target individual is known. In oneembodiment, the measured genetic data is used in the context of makingploidy determinations during prenatal genetic diagnosis. In anotherembodiment the measured genetic data is used in the context of makingploidy determinations or allele calls on embryos during in vitrofertilization. There are many methods that may be used to measure thegenetic data of the individual and/or the related individuals in theaforementioned contexts. The different methods comprise a number ofsteps, those steps often involving amplification of genetic material,addition of oligonucleotide probes, ligation of specified DNA strands,isolation of sets of desired DNA, removal of unwanted components of areaction, detection of certain sequences of DNA by hybridization,detection of the sequence of one or a plurality of strands of DNA by DNAsequencing methods. In some cases the DNA strands may refer to targetgenetic material, in some cases they may refer to primers, in some casesthey may refer to synthesized sequences, or combinations thereof. Thesesteps may be carried out in a number of different orders. Given thehighly variable nature of molecular biology, it is generally not obviouswhich methods, and which combinations of steps, will perform poorly,well, or best in various situations.

Note that in theory it is possible to target any number loci in thegenome, anywhere from one loci to well over one million loci. If asample of DNA is subjected to targeting, and then sequenced, thepercentage of the alleles that are read by the sequencer will beenriched with respect to their natural abundance in the sample. Thedegree of enrichment can be anywhere from one percent (or even less) totens fold, hundred fold, thousand fold or even many million fold. In thehuman genome there are roughly 3 billion base pairs, and nucleotides,containing approximately 75 million polymorphic loci. The more loci thatare targeted, the smaller the degree of enrichment is possible. Thefewer the number of loci that are targeted, the greater degree ofenrichment is possible, and the greater depth of read may be achieved atthose loci for a given number of sequence reads.

In one embodiment of the present disclosure, the targeting may focusentirely on SNPs. A number of commercial targeting products areavailable to enrich exons. Surprisingly, targeting exclusively SNPs isparticularly advantageous when using a method for NPD that relies onallele distributions. Currently, published methods for NPD usingsequencing, for example U.S. Pat. No. 7,888,017, a type of read countanalysis where the read counting focuses on counting the number of readsthat map to a given chromosome, where the analyzed sequence reads do notfocused on regions of the genome that are polymorphic. In one embodimentof the present disclosure, it is possible to use a targeting method thatfocuses on SNPs to enrich a genetic sample in polymorphic regions of thegenome. In one embodiment, it is possible to focus on a small number ofSNPs, for example between 1 and 100 SNPs, or a larger number, forexample, between 100 and 1,000, between 1,000 and 10,000, between 10,000and 100,000 or more than 100,000 SNPs. In one embodiment, it is possibleto focus on one or a small number of chromosomes that are correlatedwith live trisomic births, for example chromosomes 13, 18, 21, X and Y,or some combination thereof. In one embodiment, it is possible to enrichthe targeted SNPs by a small factor, for example between 1.01 fold and100 fold, or by a larger factor, for example between 100 fold and1,000,000 fold. In one embodiment of the present disclosure, it ispossible to use a targeting method to create a sample of DNA that ispreferentially enriched in polymorphic regions of the genome. In oneembodiment, it is possible to use the method to create a sample of DNAthat is preferentially enriched in a small number of SNPs, for examplebetween 1 and 100 SNPs, or a larger number of SNPs, for example, between100 and 50,000 SNPs. In one embodiment, it is possible to use the methodto create a DNA sample that is enriched in SNPs located on one or asmall number of chromosomes that are correlated with live trisomicbirths, for example chromosomes 13, 18, 21, X and Y, or some combinationthereof. In one embodiment, it is possible to use the method to create asample of DNA that is preferentially enriched in a small number of SNPs,for example between 1 and 100 SNPs, or a larger number of SNPs, forexample, between 100 and 50,000 SNPs. In one embodiment, it is possibleto use the method to create a sample of DNA that is enriched targetedSNPs by a small factor, for example between 1.01 fold and 100 fold, orby a larger factor, for example between 100 fold and 1,000,000 fold. Inone embodiment, it is possible to use this method to create a mixture ofDNA with any of these characteristics where the mixture of DNA containsmaternal DNA and also free floating fetal DNA. In one embodiment, it ispossible to use this method to create a mixture of DNA that has anycombination of these factors. For example, a mixture of DNA thatcontains maternal DNA and fetal DNA, and that is preferentially enrichedin 200 SNPs, all of which are located on either chromosome 18 or 21, andwhich are enriched an average of 1000 fold. In another example, it ispossible to use the method to create a mixture of DNA that ispreferentially enriched in 50,000 SNPs that are all located onchromosomes 13, 18, 21, X and Y, and the average enrichment per loci is200 fold. Any of the targeting methods described herein can be used tocreate mixtures of DNA that are preferentially enriched in certain loci.

In some embodiments, the method may further comprise measuring the DNAcontained in the mixed fraction using a DNA sequencer, and the DNAcontained in the mixed fraction contains a disproportionate number ofsequences from one or more chromosomes, wherein the one or morechromosomes are taken from the group comprising chromosome 13,chromosome 18, chromosome 21, chromosome X, chromosome Y andcombinations thereof.

A Method for Creating Samples that are Highly Enriched for Large Numbersof Alleles in an Unbiased Fashion, and Related Compositions of Matter

In one embodiment, the method can be used to determine genotypes (basecomposition of the DNA at specific loci) and relative proportions ofthose genotypes from a mixture of DNA molecules, where those DNAmolecules may have originated from one or a number of geneticallydistinct individuals. In one embodiment, the method can be used todetermine the genotypes at a set of polymorphic loci, and the relativeratios of the amount of different alleles present at those loci. In oneembodiment the polymorphic loci may consist entirely of SNPs. In oneembodiment, the polymorphic loci can comprise SNPs, single tandemrepeats, and other polymorphic regions. In one embodiment, the methodcan be used to determine the relative rations of different alleles at aset of polymorphic loci in a mixture of DNA, where the mixture of DNA iscomprised of DNA that originates from a mother, and DNA that originatesfrom a fetus. In one embodiment, the relative ratios of differentalleles can be determined on a mixture of DNA isolated from blood from apregnant woman. In one embodiment, the relative ratios of alleles at aset of loci can be used to determine the ploidy state of one or morechromosomes on a fetus that is gestating in the mother.

In one embodiment, the mixture of DNA molecules could be derived fromDNA extracted from multiple cells of one individual. In one embodiment,the original collection of cells from which the DNA is derived maycontain a mixture of diploid or haploid cells of the same or ofdifferent genotypes, if that individual is mosaic (germline or somatic).In one embodiment, the mixture of DNA molecules could also be derivedfrom DNA extracted from single cells. In one embodiment, the mixture ofDNA molecules could also be derived form DNA extracted from mixture oftwo or more cells of the same individual, or of different individuals.In one embodiment, the mixture of DNA molecules could be derived fromDNA isolated from biological material that has already liberated fromcells such as blood plasma, which is known to contain cell free DNA. Inone embodiment, the this biological material may be a mixture of DNAfrom one or more individuals, as is the case during pregnancy where ithas been shown that fetal DNA is present in the mixture.

In one embodiment of the present disclosure, the originating source ofDNA is cells. The mixture may contain zero or more copies of a givenchromosome. Normal healthy human cells typically contain two copies ofeach chromosome that were inherited from the two unrelated parents.These copies typically vary at many different locations (loci). Thevariations may be single nucleotide differences (SNPs), two or morenucleotide differences, insertions or deletions of one or morenucleotides, one or more exact copies of segments of DNA, which areoften positioned adjacent to one another but can be located anywhere.Common ancestral relationships may also result in segments within thenormal two copies of the DNA being identical or near identical. Germlineor somatic mosacism may result in the cells derived form one individualbeing different in one or more chromosomal locations.

Method to Accurately Determine the Relative Proportion of Alleles at aGiven Loci in a Sample:

Current sequencing approaches can be used to estimate the proportion ofalleles in the sample. These methods randomly sample sequences from apool DNA, termed shotgun sequencing. The proportion of a particularallele in the sequencing data is typically very low and can bedetermined by simple statistics. The human genome contains approximately3 billion base pairs. So, if the sequencing method used make 100 bpreads, a particular allele will be measured about once in every 30million sequence reads. In a case where two different alleles at a givenloci are present, sufficient sequencing depth will yields a relativeallele ratio that will eventually converge on the ratio with which thealleles are actually present in the mixture. More generally the relativeratios will converge on the actual ratios more slowly if there are morethan two alleles at a particular locus in the mixture.

In one embodiment of the present disclosure, the method can be used todetermine the relative ratios of two or more different haplotypes thatcontain the same set of loci in a sample of DNA. The differenthaplotypes could represent two different homologous chromosomes from oneindividual, three different homologous chromosomes from a trisomicindividual, three different homologous haplotypes from a mother and afetus where one of the haplotypes is shared between the mother and thefetus, three or four haplotypes from a mother and fetus where one or twoof the haplotypes are shared between the mother and the fetus, or othercombinations. If one or more of the haplotypes are known, or the diploidgenotypes of one or more of the individuals are known, then a set ofalleles that are polymorphic between the haplotypes can be chosen, andaverage allele ratios can be determined based on the set of alleles thatuniquely originate from each of the haplotypes.

Direct sequencing of such a sample, however, is extremely inefficient asit results in many sequences for regions that are not polymorphicbetween the different haplotypes in the sample and therefore reveal noinformation about the proportion of the two haplotypes. Described hereinis a method that specifically targets and enriches segments of DNA inthe sample that are more likely to be polymorphic in the genome toincrease the yield of allelic information obtained by sequencing. Notethat for the allele ratios measured in an enriched sample to be trulyrepresentative of the actual haplotype ratios it is critical that thereis little or no preferential enrichment of one allele as compared to theother allele at a given loci in the targeted segments. Current methodsknown in the art to target polymorphic alleles are designed to ensurethat at least some of any alleles present are detected. However, thesemethods were not designed for the purpose of measuring the allele ratioof polymorphic alleles present in the original mixture. It isnon-obvious that any particular method of target enrichment would beable to produce an enriched sample wherein the proportion of variousalleles in the enriched sample is about the same as to the ratios of thealleles in the original unamplified sample. While enrichment methods maybe designed, in theory, to accomplish such an aim, an ordinary personskilled in the art is aware that there is a great deal of stochastic ordeterministic bias in current methods. On embodiment of the methoddescribed herein allows a plurality of alleles found in a mixture of DNAthat correspond to a given locus in the genome to be amplified, orpreferentially enriched in a way that the degree of enrichment of eachof the alleles is nearly the same. Another way to say this is that themethod allows the relative quantity of the alleles present in themixture as a whole to be increased, while the ratio between the allelesthat correspond to each locus remains essentially the same as they werein the original mixture of DNA. For the purposes of this disclosure, forthe ratio to remain essentially the same, it is mean that the ratio ofthe alleles in the original mixture divided by the ratio of the allelesin the resulting mixture is between 0.5 and 1.5, between 0.8 and 1.2,between 0.9 and 1.1, between 0.95 and 1.05, between 0.98 and 1.02,between 0.99 and 1.01, between 0.995 and 1.005, between 0.998 and 1.002,between 0.999 and 1.001, or between 0.9999 and 1.0001.

In one embodiment, once a mixture has been preferentially enriched atthe set of target loci, it may be sequenced using any one of theprevious, current, or next generation of sequencing instruments thatsequences a clonal sample (a sample generated from a single molecule;examples include ILLUMINA GAIIx, ILLUMINA HISEQ, LIFE TECHNOLOGIESSOLiD, 5500XL). The ratios can be evaluated by sequencing through thespecific alleles within the targeted region. These sequencing reads canbe analyzed and counted according the allele type and the rations ofdifferent alleles determined accordingly. For variations that are one toa few bases in length, detection of the alleles will be performed bysequencing and it is essential that the sequencing read span the allelein question in order to evaluate the allelic composition of thatcaptured molecule. The total number of captured molecules assayed forthe genotype can be increased by increasing the length of the sequencingread. Full sequencing of all molecules would guarantee collection of themaximum amount of data available in the enriched pool. However,sequencing is currently expensive, and a method that can measure acertain number of allele ratios using a lower number of sequence readswill have great value. In addition, there are technical limitations tothe maximum possible length of read as well as accuracy limitations asread lengths increase. The alleles of greatest utility will be of one toa few bases in length, but theoretically any allele shorter than thelength of the sequencing read can be used. While allele variations comein all types, the examples provided herein focus on SNPs or variantscomprised of just a few neighboring base pairs. Larger variants such assegmental copy number variants can be detected by aggregations of thesesmaller variations in many cases as whole collections of SNP internal tothe segment are duplicated. Variants larger than a few bases, such asSTRs require special consideration and some targeting approaches workwhile others will not. The evaluation of the allelic rations is hereindetermined

There are multiple targeting approaches that can be used to specificallyisolate and enrich a one or a plurality of variant positions in thegenome. Typically, these rely on taking advantage of invariant sequenceflanking the variant sequence. There is prior art related to targetingin the context of sequencing where the substrate is maternal plasma(see, e.g., Liao et al., Clin. Chem.; 57(1): pp. 92-101). However, theseapproaches all use targeting probes that target exons, and do not focuson targeting polymorphic regions of the genome. In one embodiment of thepresent disclosure, the method involves using targeting probes thatfocus exclusively or almost exclusively on polymorphic regions. In oneembodiment of the present disclosure, the method involves usingtargeting probes that focus exclusively or almost exclusively on SNPs.When polymorphic targeted DNA mixtures are sequenced and analyzed usingan algorithm that determined ploidy using allele ratios, this targetingmethod is able to provide far more accurate ploidy determinations for agiven number of sequence reads. In some embodiments of the presentdisclosure, the targeted polymorphic regions consist of at least 10%SNPs, at least 20% SNPs, at least 30% SNPs, at least 40% SNPs, at least50% SNPs, at least 60% SNPs, at least 70% SNPs, at least 80% SNPs, atleast 90% SNPs, at least 95% SNPs, at least 98% SNPs, at least 99% SNPs,at least 99.9% SNPs, exclusively SNPs.

Targeted Sequencing Using Circularizing Probes

One method of measuring genetic data involves the use of circularizingprobes. Two papers that discuss a method involving circularizing probesthat can be used to measure the genomic data of the target individualinclude: Porreca et al., Nature Methods, 2007 4(11), pp. 931-936.; andalso Turner et al., Nature Methods, 2009, 6(5), pp. 315-316. The methodsdescribed in these papers may be used in combination with other methodsdescribed herein. Certain steps of the method from these two papers maybe used in combination with other steps from other methods describedherein.

In one embodiment of the methods, the genetic material of the targetindividual is amplified, and then the desired allelic geneticinformation is captured by circularizing appropriately designedoligonucleic probes, such as in the LIPs system. This may be followed bythe genetic sequence of the circularized probes being measured to givethe desired sequence data. In another embodiment, the appropriatelydesigned oligonucleotides probes may be circularized directly onunamplified genetic material of the target individual, and amplifiedafterwards. Note that a number of amplification procedures may be usedto amplify the original genetic material, or the circularized LIPs,including rolling circle amplification, MDA, or other amplificationprotocols. Different methods may be used to measure the geneticinformation on the target genome, for example using high throughputsequencing, Sanger sequencing, other sequencing methods,capture-by-hybridization, capture-by-circularization, multiplex PCR,other hybridization methods, and combinations thereof.

Once the genetic material of the individual has been measured using oneor a combination of the above methods, an informatics based method, suchas the PARENTAL SUPPORT™ method, along with the appropriate geneticmeasurements, can then be used to determination the ploidy state of oneor more chromosomes on the individual, and/or the genetic state of oneor a set of alleles, specifically those alleles that are correlated witha disease or genetic state of interest. Note that the use of LIPs hasbeen reported for multiplexed capture of genetic sequences, followed bygenotyping with sequencing. However, the use of sequencing dataresulting from a LIPs-based strategy for the amplification of thegenetic material found in a single cell, a small number of cells, orextracellular DNA, has not been used for the purpose of determining theploidy state of a target individual.

Applying an informatics based method to determine the ploidy state of anindividual from genetic data as measured by hybridization arrays, suchas the ILLUMINA INFINIUM array, or the AFFYMETRIX gene chip has beendescribed in documents references elsewhere in this document. However,the method described herein shows improvements over methods describedpreviously in the literature. For example, the LIPs based approachfollowed by high throughput sequencing unexpectedly provides bettergenotypic data due to the approach having better capacity formultiplexing, better capture specificity, better uniformity, and lowallelic bias. Greater multiplexing allows more alleles to be targeted,giving more accurate results. Better uniformity results in more of thetargeted alleles being measured, giving more accurate results. Lowerrates of allelic bias result in lower rates of miscalls, giving moreaccurate results. More accurate results result in an improvement inclinical outcomes, and better medical care.

In one embodiment of the present disclosure, a pregnant mother wouldlike to determine if her fetus is afflicted with any gross chromosomalabnormalities. She goes to her doctor, and gives a sample of her blood,and she and her husband gives samples of their own DNA from cheek swabs.A laboratory researcher genotypes the parental DNA using the MDAprotocol to amplify the parental DNA, and ILLUMINA INFINIUM arrays tomeasure the genetic data of the parents at a large number of SNPs. Theresearcher then spins down the blood, takes the plasma, and isolates asample of free-floating DNA using size exclusion chromatography.Alternately, the researcher uses one or more fluorescent antibodies,such as one that is specific to fetal hemoglobin to isolate a nucleatedfetal red blood cell. The researcher then takes the isolated or enrichedfetal genetic material and amplifies it using a library of 70-meroligonucleotides appropriately designed such that two ends of eacholigonucleotide corresponded to the flanking sequences on either side ofa target allele. Upon addition of a polymerase, ligase, and theappropriate reagents, the oligonucleotides underwent gap-fillingcircularization, capturing the desired allele. An exonuclease was added,heat-inactivated, and the products were used directly as a template forPCR amplification. The PCR products were sequenced on an ILLUMINA GENOMEANALYZER. The sequence reads were used as input for the PARENTALSUPPORT™ method, which then predicted the ploidy state of the fetus.

It is important to note that LIPs may be used as a method for targetingspecific loci in a sample of DNA for genotyping by methods other thansequencing. For example, LIPs may be used to target DNA for genotypingusing SNP arrays or other DNA or RNA based microarrays.

The Use of Linked Inverted Probes for Genotyping SNPs, Repeat Expansionand Large Deletions Alleles

In one embodiment of the present disclosure, inverted probes may be usedto genotype a wide variety of loci, for example, not just SNPs, but alsolarge repeats such as triple repeats and tandem repeats, or largedeletions. There are a number of diseases that are characterized by suchrepeats and/or deletions. Methods of amplification and genotyping thathave been described in the literature have a number of problems thatpreclude their use in a large scale multiplexed fashion.

The LIPs technologies, of which MIPs and PADLOCK PROBES are a subset,share a common feature in that they involve a synthesized DNA fragmentin which the ends are specifically constructed to form complementarybase-pairing to a target DNA under suitable reaction conditions, hereincalled the “probe,” or the “pre-circularized probe,” or the“pre-circularizing probe,” or the “circularizing probe.” Furthermore theends of said probe are designed in a manner such that the 5-prime (5′)and 3-prime (3′) ends of the probe are oriented towards one anotherannealing of the probe, herein generally called “inverted-linkedprobes,” to the target DNA, herein called “the template.” Consequently,addition of dNTPs, polymerase, ligase, and suitable buffers, results inpolymerization from the 3′ end of the probe, herein referred to as “theextension,” filling in the gap between the 3′ and 5′ ends of the probewith nucleotides complementary to the template DNA. Once the gap iscompletely filled, ligase catalyzes the formation of a covalentphosphodiester bond between the now adjacent 3′ and 5′ ends of the probecreating a complete circular molecule of DNA. There is no necessaryupper limit to size of the gap between the 3′ and 5′ ends of thefragment that can be filled with complementary bases. A practical upperlimit may be determined by the reaction conditions, the processivity ofthe polymerase, and the ability to amplify the fragment by subsequentPCR based methods.

The region of interest between the original 3′ and 5′ ends of thefragment may be amplified by various techniques after the circle, nowintertwined with the template, has been released from the target DNA.Release may be achieved by breakage of the template molecule or bybreakage of the now circular probe. This may be done along the backboneof the probe as not to disturb the newly polymerized target sequence.Amplification of the target region, herein referred to as “probeamplification,” may then be accomplished by various PCR techniques or byrolling circle amplification (if the probe remains a circle).

In some embodiments of the present disclosure, this technique may beused to accomplish specific targeting and amplification of sequences inthe genome. In addition, this technique enables efficient multiplexing,i.e. mixing in the same reaction vessel, of probes to distinct templatetargets. The physical linking of the two complementary sequences into asingle probe backbone has the effect of limiting cross-reactions betweenunintended combinations of target sequences, as typically occurs withmultiplex PCR. All of the newly extended probes may be amplifiedsimultaneously using amplification primers or techniques common to allthe probes. The resulting amplified sequences may be analyzed for size,size distribution, allele constitution, or specific sequence by variousmethods. Gel separation can reveal size and size distribution.Microarrays and quantitative PCR can reveal allele constitution usingeither target specific hybridization or probe specific hybridization,where probes are individually tagged with distinct sequences. Sequencingby methods, such as the Sanger dideoxy method, could also revealsequence in certain circumstances. Sequencing using other methods, suchas the clonal (e.g. polony, bridge) or single molecule sequencingmethods, can reveal the sequence as well as counts of individualmolecules in the amplified pool. Furthermore, sequencing enables mixingand sequencing multiple probe amplification pools from differentindividuals. One way to accomplish this would be for each initial probepool applied to a sample to either contain a different synthesizedsequence that could be used differentiate different samples, or aspecific distinguishing sequence could be added and covalently linked tothe products of the probe amplification. These sample specific sequencescould then be detected during the sequence process allowingdisambiguation as to from which sample each particular sequence instancewas derived. In one embodiment, one could add probes afteramplification; the order and timing of addition of the various reagentsand probes may be different.

In one embodiment, LIPs may be used to detect certain disease allelesthat are not easily detected using other PCR based techniques. Allelesof certain diseases are not amenable to PCR based amplification. Forexample, the disease Fragile X, an X-linked disorder, is caused bytandem expansion of a tri-nucleotide repeat of the DNA nucleotides CGG.When the number of repeats is greater than 45 repeats become unstableand become prone to further expansion. A chromosome with greater than200 repeats is considered to have the full mutation. Both males, whoonly have one X chromosome, and heterozygous females, will showcharacteristics of the disease at repeats greater than about 200triplets in size. One challenge in PCR based screening techniques isthat PCR, while usually capable of amplifying the normal size range ofalleles, will often fail to amplify expanded alleles due the highlyrepetitive nature of the DNA. Consequently, PCR based tests used onheterozygous individuals may yield a false negative test result whenonly the normal allele is detected.

In one embodiment, this problem may be solved by using at least two, butalso possibly three or more distinct linked inverted probes. The firstprobe may be designed so that both ends are complementary to the DNAsequence flanking the repetitive sequence prone to expansion, hereincalled the “spanning probe.” Upon binding, this probe would straddle theentire repeat region, enabling detection and amplification of the normalallele and some size range of expanded alleles. A second probe, hereincalled the “non-spanning probe,” may be designed such that one end ofthe probe is complementary to the non-repetitive sequence upstream ofthe repeat and the other end complementary to the repeat itself.Similarly, another non-spanning probe may also be designed with one endcomplementary to the downstream non-repetitive DNA sequence and theother end complementary to the repetitive sequence. The spanning probewould be expected to extend and amplify in the presence of the normalallele as well as some size range of expanded alleles. However, for thesame reasons that PCR fails at the largest size ranges of these repeatalleles, this probe may fail at the larger size ranges of the expandedallele. However, the non-spanning probes allow detection of thesealleles. These probes bind to one side of the repeat, anchoring theprobe while the other end of the probe is free to find to bind tonumerous places within the repeat. Extension and amplification of theseprobes then yields a distribution of differently sized fragments. Thesize distribution can be detected through various methods including DNAseparation techniques (e.g. agarose gel), or by direct sequencing of theamplified probes any clonal sequencing method. Collectively, thespanning and one or both of the non-spanning probes may be used todetect the presence of all possible genotypes, by sequencing, forexample.

For an allele that can be extended and amplified by the spanning probe,the size of the allele may be readily observed upon analysis. If in anormal individual there are two different size normal alleles, both maybe detectable by the spanning probe. If the size of one or both allelesis abnormal, but still within the limits of detection of the spanningprobe, then again both alleles may be detectable. If the one or both ofthe alleles is so large such that it cannot be extended or amplifiedwith the spanning probe, then the data from one or both of thenon-spanning probes may be used to determine or estimate the repeatlength, as both an internal positive control and as a means todemonstrate the presence of an allele that is larger than normal sizerage. With normal PCR methods, large repeats simply fail to amplify.Consequently, in the circumstance where an individual is heterozygousfor a normal allele and a greatly expanded allele and the expandedallele fails to amplify, then the individual will falsely appear to behomozygous for the normal allele. However, the combination of thespanning probe and non-spanning probes allow detection of the normalallele and observation of the expanded allele. Even though thenon-spanning probe may not extend and amplify the largest possiblefragments, the presence of any bands larger than the normal size willindicate the presence of an abnormal allele.

In one embodiment, LIPs may be used to detect large deletions withdefined or potentially poorly defined end points. Large deletions areresponsible for a number of important human disorders. For example,Hemophilia A can be caused by large deletions of varying size in theFactor VIII gene on the X chromosome; Duchenne and Becker MuscularDystrophy can be caused by large deletions of varying size in the DMDgene, also on the X chromosome). There is a challenge in detecting largemutations using traditional PCR methods. Two PCR based approaches fordetecting large deletions are (a) to design multiple PCR within andflanking the region of the deletion and (b) design a set of PCR assayincluding ones that spans the entire deletion (both endpoints) as wellas each endpoint individually. In (a), an individual that is homozygousor hemizygous for the deletion, the PCR assays within the mutation mayfail to amplify while the ones flanking the mutation may amplify.However, this method cannot be used to detect a heterozygote as all PCRassays will amplify. In (b) if the endpoints of the deletion are knownit is possible to design a PCR assay that can yield a product that spansthe breakpoint of the mutation yielding a chimeric fragment in thepresence of the mutation. In the normal allele, this PCR amplificationwill likely fail due to the large distances involved (many kilobases).However, the normal allele can be detected through the use of assaysthat span just one endpoint. When the exact endpoints of the deletionare not known it can be much more challenging to design a PCR assaycapable of detecting various forms of the deletion reliably. Trial anderror must typically be employed in each instance. In one embodiment,the ability to multiplex linked inverted probes can be used to design aseries of probes can be created that can detect deletions of any size.

In one embodiment, to detect deletions of any size, one may design acollection of linked inverted probes that spanning various distancesfrom one or both of the farthest known endpoints, in addition to a smallnumber of probes spaced at various intervals to detect the normalallele. Each of the spanning probes may have one end complementary tothe non-deleted region. The other end of each distinct probe may becomplementary to some region at some variable large distance fromnon-deleted end. The distance between the probe ends could be too largeto extend and amplify using typical approaches, but in the presence of alarge deletion, a previously distant binding site for one or more of theprobes could be brought to within distance that could be amplified andextended. The resulting product may be detected by an array (detectingpresence absence only of an amplified probe) or by sequencing aspreviously described. Sequencing of the probe may reveal a chimericfragment of DNA with the two previously flanking DNA sequences nowflanking one another. The number of probes required could be determinedby the length of the gap that could be extended, amplified, and extendedas well as the maximum possible length of the deletion.

LIPs and Sequencing

The use of LIPs followed by sequencing as part of a method for allelecalling or ploidy calling for the purpose of prenatal diagnosis mayconfer a number of unexpected advantages. In some embodiments of thepresent disclosure, the method involves measuring genetic data for usewith an informatics based method, such as PARENTAL SUPPORT™ (PS). Theultimate outcome of some of the embodiments is the actionable geneticdata of an embryo or a fetus. The algorithms behind the PS method takethe measured genetic data of the target individual, often an embryo orfetus, and the measured genetic data from related individuals, and areable to increase the accuracy with which the genetic state of the targetindividual is known. In one embodiment, the measured genetic data isused in the context of making ploidy determinations during prenatalgenetic diagnosis. In another embodiment the measured genetic data isused in the context of making ploidy determinations or allele calls onembryos during in vitro fertilization. There are many methods that maybe used to measure the genetic data of the individual and/or the relatedindividuals in the aforementioned contexts. The different methodscomprise a number of steps, those steps often involving amplification ofgenetic material, addition of oligonucleotide probes, ligation ofspecified DNA strands, isolation of sets of desired DNA, removal ofunwanted components of a reaction, detection of certain sequences of DNAby hybridization, detection of the sequence of one or a plurality ofstrands of DNA by DNA sequencing methods. In some cases the DNA strandsmay refer to target genetic material, in some cases they may refer toprimers, in some cases they may refer to synthesized sequences, orcombinations thereof. These steps may be carried out in a number ofdifferent orders. Given the highly variable nature of molecular biology,it is generally not obvious which methods, and which combinations ofsteps, will perform poorly, well, or best in various situations.

Disclosed herein is a method to overcome the disadvantages of thecircularizing probes methods known in the literature. In one embodimentof the present disclosure, the genetic material of the target individualis amplified before circularizing probes are added. In this situation,the small amount of genetic material may be amplified using a widevariety of techniques, for example, multiple displacement amplificationor polymerase chain reaction. Other methods of amplification areoutlined herein. Once the genetic material from the target individualhas been amplified, methods described in the literature that usecircularizing probes. Note that the methods known in the art for usingcircularizing probes involve adding the probes to unamplified, genomicDNA.

For example, after the preamplification step of the target geneticmaterial, the amplified the nucleic acid sequence may be mixed with aprobe that can hybridize with two neighboring regions of the targetsequence, one on either side. After hybridization, the ends of the probemay be connected by adding a polymerase, a means for ligation, and anynecessary reagents to allow the circularization of the probe. Aftercircularization, an exonuclease may be added to digest tonon-circularized genetic material, followed by detection of thecircularized probe.

The detection of the circularized probe may be done in a number of ways,as described in the literature. For example, it may be isolated, forexample by chromatography, it may be amplified, for example by rollingcircle amplification, and it may be detected by hybridization, forexample using ILLUMINA BEAD ARRAYS or AFFYMETRIX GENECHIP, or it may besequenced using Sanger sequencing, or a high throughput sequencingplatform such as the ILLUMINA SOLEXA GENOME ANALYZER.

In some embodiments the detection of the target genetic material may bedone in a multiplexed fashion. The number of genetic target sequencesthat may be run in parallel can range from one to ten, ten to onehundred, one hundred to one thousand, one thousand to ten thousand, tenthousand to one hundred thousand, one hundred thousand to one million,or one million to ten million.

In some embodiments, this method may be used to genotype a single cell,a small number of cells, two to five cells, six to ten cells, ten totwenty cells, twenty to fifty cell, fifty to one hundred cells, onehundred to one thousand cells, or a small amount of extracellular DNA,for example from one to ten picograms, from ten to one hundredpictograms, from one hundred pictograms to one nanogram, from one to tennanograms, from ten to one hundred nanograms, or from one hundrednanograms to one microgram.

In one embodiment, the method may be used in the context of in vitrofertilization, where it may be desirable to genotype a single cellblastomere biopsied from a cleavage stage embryo for the purposes ofdetermining the genetic state of the embryo. Or, it may be used togenotype a small number of cells biopsied from the trophectoderm, orfrom the inner cell mass, of a day 5 embryo, also for the purposes ofdetermining the genetic state of the embryo. In another embodiment, itmay be used in the context of non-invasive prenatal diagnosis togenotype isolated single fetal cells found in maternal blood. In anotherembodiment, in the context of prenatal diagnosis, it may be used togenotype free floating DNA found in maternal blood. In all of theseembodiments, the target genetic data that is measured is expected to beactionable, and may be used to make clinical decisions.

Reducing Allele Bias Using Circularizing Probes

One method to target specific locations for sequencing is to synthesizeprobes in which the 3′ and 5′ ends of the probes anneal to target DNA atlocations adjacent to and on either side of the targeted region, in aninverted manner, such that the addition of DNA polymerase and DNA ligaseresults in extension from the 3′ end, adding bases to single strandedprobe that are complementary to the target molecule (gap-fill), followedby ligation of the new 3′ end to the 5′ end of the original proberesulting in a circular DNA molecule that can be subsequently isolatedfrom background DNA. The probe ends are designed to flank the targetedregion of interest. One aspect of this approach is commonly called MIPSand has been used in conjunction with array technologies to determinethe nature of the sequence filled in. One drawback to the use of MIPs inthe context of measuring allele ratios is that the hybridization,circularization and amplification steps do not happed at equal rates fordifferent alleles at the same loci. This results in measured alleleratios that are not representative of the actual allele ratios presentin the original mixture.

In one embodiment of the present disclosure, this approach has beenmodified to be easily amenable to sequencing as a means of interrogatingthe filled in sequence. In order to retain the original allelicproportions of the original sample at least one key consideration mustbe taken into account. The variable positions among different alleles inthe gap-fill region must not be too close to the probe binding sites asthere can be initiation bias by the DNA polymerase resulting indifferential of the variants. Another consideration is that additionalvariations may be present in the probe binding sites that are correlatedto the variants in the gap-fill region which can result unequalamplification from different alleles. In one embodiment of the presentdisclosure, the 3′ ends and 5′ ends of the pre-circularized probe aredesigned to hybridize to bases that are one or a few positions away fromthe variant positions (polymorphic regions) of the targeted allele. Thenumber of bases between the polymorphic region (SNP or otherwise) andthe base to which the 3′ end and/or 5′ of the pre-circularized probe isdesigned to hybridize may be one base, it may be two bases, it may bethree bases, it may be four bases, it may be five bases, it may be sixbases, it may be seven to ten bases, it may be eleven to fifteen bases,or it may be sixteen to twenty bases. The forward and reverse primersmay be designed to hybridize a different number of bases away from thepolymorphic region. Circularizing probes can be generated in largenumbers with current DNA synthesis technology allowing very largenumbers of probes to be generated and potentially pooled, enablinginterrogation of many loci simultaneously. It has been reported to workwith more than 300,000 probes.

Note that this strategy maybe equally well used with PCR primers. In oneembodiment, in order to retain the original allelic proportions of theoriginal sample the variable positions among different alleles in theregion adjacent to the probe binding site must not be too close to theprobe binding sites as there can be initiation bias by the DNApolymerase resulting in differential of the variants. In one embodimentof the present disclosure, the 3′ end of the PCR probe is designed tohybridize to bases that are one or a few positions away from the variantpositions (polymorphic regions) of the targeted allele. The number ofbases between the polymorphic region (SNP or otherwise) and the base towhich the 3 end of the PCR probe is designed to hybridize may be onebase, it may be two bases, it may be three bases, it may be four bases,it may be five bases, it may be six bases, it may be seven to ten bases,it may be eleven to fifteen bases, or it may be sixteen to twenty bases.The forward and reverse primers may be designed to hybridize a differentnumber of bases away from the polymorphic region.

Targeted Sequencing Using Capture by Hybridization Approaches

Targeting of a specific set of sequences in a target genome can beaccomplished in a number of ways. Elsewhere in this document is adescription of how LIPs can be used to target a specific set ofsequences, but in all of those applications, other targeting methods canbe used equally well for the same ends. One example of another targetingmethod is the capture by hybridization approach. Some examples ofcommercial capture by hybridization technologies include AGILENT's SURESELECT and ILLUMINA's TRUSEQ. In capture by hybridization, a set ofoligonucleotides that is complimentary or mostly complimentary to thedesired targeted sequences is allowed to hybridize to a mixture of DNA,and then physically separated from the mixture. Once the desiredsequences have hybridized to the targeting oligonucleotides, the effectof physically removing the targeting oligonucleotides is to also removethe targeted sequences. Once the hybridized oligos are removed, they canbe heated to above their melting temperature and they can be amplified.Some ways to physically remove the targeting oligonucleotides is bycovalently bonding the targeting oligos to a solid support, for examplea magnetic bead, or a chip. Another way to physically remove thetargeting oligonucleotides is by covalently bonding them to a molecularmoiety with a strong affinity for another molecular moiety. And exampleof such a molecular pair is biotin and streptavidin, such as is used inSURE SELECT. Thus that targeted sequences could be covalently attachedto a biotin molecule, and after hybridization, a solid support withstreptavidin affixed can be used to pull down the biotinylated oligos,to which are hybridized the targeted sequences.

Another method of targeting is hybrid capture. In this method probesthat are complementary to the targets of interest are synthesized andthen used to hybridize to the target molecules. The hybridized moleculescan be separated by various published techniques from the non-hybridized(untargeted) molecules. This probe was originally developed to targetand enrich large fractions of the genome with relative uniformitybetween targets. In this application, it is important that all targetsbe amplified with enough uniformity that all regions could be detectedby sequencing, however, no regard was paid to retaining the proportionof alleles in original sample. Following capture, the alleles present inthe sample can be determined by direct sequencing of the capturedmolecules. The ratios can be evaluated by sequencing through thespecific alleles within the targeted region. These sequencing reads canbe analyzed and counted according the allele type. However, using thecurrent technology, the measured allele ratios of the captured sequencesat a given loci are typically not representative of the original alleleratios.

Probe length, target molecule length, and sequencing read length can allbe adjusted to improve the amount of useful enrichment and the uniformlyof the enrichment of the different alleles in the original sample

In one embodiment, detection of the alleles is performed by sequencing.In order to capture the allele identity at the polymorphic site, it isessential that the sequencing read span the allele in question in orderto evaluate the allelic composition of that captured molecule. Since thecapture molecules are often of variable lengths upon sequencing cannotbe guaranteed to overlap the variant positions unless the entiremolecule is sequenced. However, cost considerations as well as technicallimitations as to the maximum possible length and accuracy of sequencingreads make sequencing the entire molecule unfeasible. In one embodiment,the read length can be increased from about 30 to about 50 or about 70bases can greatly increase the number of reads that overlap the variantpositions within the targeted sequences.

Another way to increase the number of reads that interrogate theposition of interest is to decrease the length of the probe, as long asit does not result in bias in the underlying enriched alleles. Thelength of the synthesized probe should be long enough such that twoprobes designed to hybridize to two different alleles found at one locuswill hybridize with near equal affinity to the various alleles in theoriginal sample. Currently, methods known in the art describe probesthat are longer than 90 bases. However, if the allele is one or a fewbases, a probe between 25 and 90 bases is sufficient to ensure equalenrichment from all alleles. When the mixture of DNA that is to beenriched using the hybrid capture technology is a mixture containingfree floating DNA isolated from blood, for example maternal blood, theaverage length of DNA is quite short, typically less than 200 bases.Using shorter probes results in a greater chance that the hybrid captureprobes will capture desired DNA fragments. Larger variations may requirelonger probes. In one embodiment, the variations of interest are one (aSNP) to a few bases in length. In one embodiment, targeted regions inthe genome can be preferentially enriched using hybrid capture probeswherein the hybrid capture probes are of a length below 90 bases, andcan be as low as 80 bases, as low as 70 bases, as low as 60 bases, aslow as 50 bases, as low as 40 bases, as low as 30 bases, or as low as 25bases. In one embodiment, to increase the chance that the desired alleleis sequenced, the length of the probe that is designed to hybridize tothe regions flanking the polymorphic allele location can be decreasedfrom above 90 bases, to about 80 bases, or to about 70 bases, or toabout 60 bases, or to about 50 bases, or to about 40 bases, or to about30 bases, or to about 25 bases.

There is a minimum overlap between the synthesized probe and the targetmolecule in order to enable capture. This synthesized probe can be madeas short as possible while still being larger than this minimum requiredoverlap. The effect of using a shorter probe length to target apolymorphic region is that there will be more molecules that overlappingthe target allele region. The state of fragmentation of the original DNAmolecules also affects the number of reads that will overlap thetargeted alleles. Some DNA samples such as plasma samples are alreadyfragmented due to biological processes that take place in vivo. However,samples with longer fragments by benefit from fragmentation prior tosequencing library preparation and enrichment. When both probes andfragments are short (˜60-80 bp) maximum specificity may be achievedrelatively few sequence reads failing to overlap the critical region ofinterest.

In one embodiment, the hybridization conditions can be adjusted tomaximize uniformity in the capture of different alleles present in theoriginal sample. In one embodiment, hybridization temperatures aredecreased to minimize differences in hybridization bias between alleles.Methods known in the art avoid using lower temperatures forhybridization because lowering the temperature has the effect ofincreasing hybridization of probes to unintended targets. However, whenthe goal is to preserve allele ratios with maximum fidelity, theapproach of using lower hybridization temperatures provides optimallyaccurate allele ratios, despite the fact that the current art teachesaway from this approach. Hybridization temperature can also be increasedto require greater overlap between the target and the synthesized probeso that only targets with substantial overlap of the targeted region arecaptured. In some embodiments of the present disclosure, thehybridization temperature is lowered from the normal hybridizationtemperature to about 40° C., to about 45° C., to about 50° C., to about55° C., to about 60° C., to about 65, or to about 70° C.

In one embodiment, the hybrid capture probes can be designed such thatthe region of the capture probe with DNA that is complementary to theDNA found in regions flanking the polymorphic allele is not immediatelyadjacent to the DNA that is immediately adjacent to the polymorphicregion. Instead, the capture probe can be designed such that the regionof the capture probe that is designed to hybridize to the DNA flankingthe polymorphic region of the target is separated from the portion ofthe capture probe that will be in van der Waals contact with thepolymorphic region by a small molecular moiety that is equivalent inlength to one or a small number of bases, and which has a binding energythat is roughly independent of the sequence to which is in contact. Inone embodiment, the hybrid capture probe is designed to hybridize to aregion that is flanking the polymorphic allele but does not cross it;this may be termed a flanking capture probe. The length of the flankingcapture probe may be as low as about 120 bases, as low as about 110bases, as low as about 100 bases, as low as about 90 bases, and can beas low as about 80 bases, as low as about 70 bases, as low as about 60bases, as low as about 50 bases, as low as about 40 bases, as low asabout 30 bases, or as low as about 25 bases.

Targeted Sequencing Using PCR Approaches

In some embodiments, PCR can be used to target specific locations of thegenome. In plasma samples, the original DNA is highly fragmented(˜100-200 bp, 150 peak). In PCR, both forward and reverse primers mustanneal to the same fragment to enable amplification. Therefore, if thefragments are short, the PCR assays must amplify relatively shortregions as well. Like MIPS, if the polymorphic positions are too closethe polymerase binding site, it could result in biases in theamplification from different alleles. Currently, PCR primers that targetpolymorphic regions, such as SNPs, are typically designed such that the3′ end of the primer will hybridize to the base immediately adjacent tothe polymorphic base or bases. In one embodiment of the presentdisclosure, the 3′ ends of both the forward and reverse PCR primers aredesigned to hybridize to bases that are one or a few positions away fromthe variant positions (polymorphic regions) of the targeted allele. Thenumber of bases between the polymorphic region (SNP or otherwise) andthe base to which the 3′ end of the primer is designed to hybridize maybe one base, it may be two bases, it may be three bases, it may be fourbases, it may be five bases, it may be six bases, it may be seven to tenbases, it may be eleven to fifteen bases, or it may be sixteen to twentybases. The forward and reverse primers may be designed to hybridize adifferent number of bases away from the polymorphic region.

PCR assay can be generated in large numbers, however, the interactionsbetween different PCR assays makes it difficult to multiplex them beyondabout one hundred assays. Various complex molecular approaches can beused to increase the level of multiplexing, but it may still be limitedto fewer than 1000 assays per reaction. Samples with large quantities ofDNA can be split among multiple sub-reactions and then recombined beforesequencing. For samples where either the overall sample or somesubpopulation of DNA molecules is limited, splitting the sample wouldintroduce statistical noise. In one embodiment, a small or limitedquantity of DNA may refer to an amount below 10 pg, between 10 and 100pg, between 100 pg and 1 ng, between 1 and 10 ng, or between 10 and 100ng. Note that while this method is particularly useful on small amountsof DNA where other methods that involve splitting into multiple poolscan cause significant problems related to introduced stochastic noise,this method still provides the benefit of minimizing bias when it is runon samples of any quantity of DNA. In these situations apre-amplification step may be used to increase the overall samplequantity. However, this pre-amplification step should not appreciablyalter the allelic ratios.

In one embodiment, the method can generate hundreds to thousands of PCRproducts (can be 10,000 and more), e.g. for genotyping by sequencing orsome other genotyping method, from limited samples such as single cellsor DNA from body fluids. Currently, performing multiplex PCR reactionsof more than 5 to 10 targets presents a major challenge and is oftenhindered by primer side products, such as primer dimers, and otherartifacts. In next generation sequencing the vast majority of thesequencing reads would sequence such artifacts and not the desiredtarget sequences in a sample. In general, to perform targeted sequencingof multiple (n) targets of a sample (greater than 10, 50 or 1000's), onecan split the sample into n parallel reactions that amplify oneindividual target, which is problematic for samples with a limitedamount of DNA. This has been performed in PCR multiwell plates or can bedone in commercial platforms such as the Fluidigm Access Array (48reactions per sample in microfluidic chips) or droplet PCR by Rain DanceTechnologies (100s to a few thousands of targets). Described here is amethod to effectively amplify many PCR reactions, that is applicable tocases where only a limited amount of DNA is available. In oneembodiment, the method may be applied for analysis of single cells, bodyfluids, biopsies, environmental and/or forensic samples.

Solution:

A) Generate and amplify a library with adaptor sequences on both ends ofDNA fragments. Divide into multiple reactions after libraryamplification.

B) Generate (and possibly amplify) a library with adaptor sequences onboth ends of DNA fragments. Perform 1000-plex amplification of selectedtargets using one target specific “Forward” primer per target and onetag specific primer. One can perform a second amplification from thisproduct using “Reverse” target specific primers and one (or more) primerspecific to a universal tag that was introduced as part of the targetspecific forward primers in the first round.

C) Perform a 1000-plex preamplification of selected target for a limitednumber of cycles. Divide the product into multiple aliquots and amplifysubpools of targets in individual reactions (for example, 50 to500-plex, though this can be used all the way down to singleplex). Poolproducts of parallel subpools reactions.

D) During these amplifications primers may carry sequencing compatibletags (partial or full length) such that the products can easily besequenced.

There is significant diagnostic value in accurately determining therelative proportion of alleles present in a sample. The interpretationof the result depends on the source of the material. In some embodimentsof the present disclosure, the allelic ratio information can be used todetermine the genetic state of an individual. In some embodiments of thepresent disclosure, this information can be used to determine thegenetic state of a plurality of individuals from one DNA sample, whereinthe DNA sample contains DNA from each of the plurality of individuals.In one embodiment, the allelic ratio information can be used todetermine copy number of whole chromosomes from individual cells, orbulk samples. In one embodiment, the allelic ratio information can beused to determine copy number of parts, regions, or segments ofchromosomes individual cells, or bulk samples. In one embodiment, theallelic ratio information can be used to determine the relativecontribution of different cell types in mosaic samples. In oneembodiment, the allelic ratio information can be used to determine thefraction of fetal DNA in maternal plasma samples as well as thechromosome copy number of the fetal chromosomes.

Generation of Targeted Sequencing Libraries by PCR of Greater than 100Targets

We are looking for a protocol that permits the targeted amplification ofover a hundred to several thousand or more target sequences (e.g. SNPloci) from genomic DNA obtained from plasma. The amplified sample shouldbe free of primer dimer products and be preferably unbiased betweenalleles and target loci. If during or after amplification the productsare appended with sequencing compatible adaptors, analysis of theseproducts can be performed by next-gen sequencing.

The initial solution to the problem of amplifying e.g. 5000 SNPs is toperform one 5000-plex PCR amplification of the total plasma DNA sample.However, experience shows that such high multiplexing (1042-plex wasattempted in house) leads to the generation of primer dimer productsthat are far in excess of the desired amplification products. These canbe reduced empirically by eliminating primers that form these mischiefproducts and by performing in silico selection of primers. However, thelarger the number of assays, the more insurmountable this problembecomes.

One solution is to split the 5000-plex reaction into severallower-plexed amplifications, e.g. one hundred 50-plex or fifty 100-plexreactions. However, if the sample DNA is limited, such as innon-invasive prenatal diagnostics from pregnancy plasma, dividing thesample between multiple reactions should be avoided. Note that thisapproach could be used to perform targeted amplification in a mannerthat would result in low amounts of allelic bias for 50-500 loci, for500 to 5,000 loci, for 5,000 to 50,000 loci, or even for 50,000 to500,000 loci.

Described herein is a method to first globally amplify the plasma DNA ofa sample and then divide the sample up into multiple multiplexed targetenrichment reactions with moderate target sequences per reaction. In oneembodiment, the method can be used for preferentially enriching a DNAmixture at a plurality of loci, the method comprising generating andamplifying a library from a mixture of DNA where the molecules in thelibrary have adaptor sequences ligated on both ends of the DNAfragments, dividing the amplified library into multiple reactions,performing a first round of multiplex amplification of selected targetsusing one target specific “forward” primer per target and one or aplurality of adaptor specific universal “reverse” primers. In oneembodiment, the method may further comprise performing a secondamplification using “reverse” target specific primers and one or aplurality of primers specific to a universal tag that was introduced aspart of the target specific forward primers in the first round. In oneembodiment, the method may be used for preferentially enriching a DNAmixture at a plurality of loci, the method comprising performing amultiplex preamplification of selected targets for a limited number ofcycles, dividing the product into multiple aliquots and amplifyingsubpools of targets in individual reactions, and pooling products ofparallel subpools reactions. In one embodiment, the primers carrypartial or full length sequencing compatible tags.

Workflow:

-   -   1. Extract plasma DNA    -   2. Prepare fragment library with universal adaptors on both ends        of fragments.    -   3. Amplify library using universal primers specific to the        adaptors.    -   4. Divide the amplified sample “library” into multiple aliquots.        Perform multiplex (e.g. 100-plex, or 1000-plex with one target        specific primer per target and a tag-specific primer)        amplifications on aliquots.    -   5. Pool aliquots of one sample.    -   6. Barcode sample if not already done.    -   7. Mix samples, adjust concentration.    -   8. Perform sequencing.

The workflow may contain multiple sub-steps that comprise one of thelisted steps (e.g. step 2. Library preparation may comprise 3 enzymaticsteps (blunt ending, dA tailing and adaptor ligation) and 3 purificationsteps).

Steps of the workflow may be combined, divided up or performed indifferent order (e.g. bar coding and pooling of samples).

It is important to note that the amplification of a library can beperformed in such a way that it is biased to amplify short fragmentsmore efficiently. In this manner it is possible to preferentiallyamplify shorter sequences, e.g. mono-nucleosomal DNA fragments as thecell free fetal DNA (of placental origin) found in the circulation ofpregnant women.

PCR Assays:

-   -   Can have the tags for sequencing (usually a truncated form of        15-25 bases). After multiplexing, PCR multiplexes of a sample        are pooled and then the tags are completed (including bar        coding) by a tag-specific PCR (could also be done by ligation).    -   The full sequencing tags can be added in the same reaction as        the multiplexing. In the first cycles targets are amplified with        the target specific primers, subsequently the tag-specific        primers take over to complete the SQ-adaptor sequence.    -   The PCR primers carry no tags. After m.p. PCR the sequencing        tags are appended to the amplification products by ligation.

Sequencing Results:

-   -   The 12 samples were pooled at equal volumes    -   Pool cleaned into 100 ul Elution buffer    -   Pool diluted to 30 nM (was 75 nM)    -   Sent for sequencing    -   QC by qPCR        preparation of 15 cy replicates        (Orange: 8 replicates with barcodes 5 to 12)    -   15 cycles STA        -   (RED STA protocol: 95 C×10 min; 95 C×15 s, 65 C×1 min, 60            C×4 min, 65 C×30 s, 72 C×30 s; 72 C×2 min)        -   Used the 50 nM primers reactions        -   Performed a first ExoSAP straight from product→failed to            remove all primers (Bioanalyzer): just leave this step out            in the future.        -   Dilute 1/10 (adding 90 ul H₂O)        -   2 ul in 14 ul ExoSAP reaction dilute to 50 ul=1/25 dilution            in this step=total 1/250    -   Append SQ tags (longer, full F-SQ and R-m.p. adaptor without        barcodes):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-m.p.; concentrations: 200            nM?        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×30 s, 65 C×15 s, 72            C×30 s; 72 C×2 min        -   Add 90 ul H2O, use 1 ul for next step, primer carry over            will be 1/100 of conc in this reaction    -   Barcoding PCR (p.9 quick book):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-BC1 to 12-lib.;            concentrations: 1 uM        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×15 s, 72 C×30 s; 72            C×2 min        -   Add 40 ul H₂O            →check 1 ul on Bioanalyzer DNA1000 chip→pool samples→clean            up→Bioanalyzer, adjust conc→sequencing            prep of 30 cy replicate            (Yellow: 1 replicates with barcode 4 into sequencing)    -   30 cycles STA        -   (Yellow STA protocol: 95 C×10 min; 95 C×15 s, 65 C×1 min, 60            C×4 min, 65 C×30 s, 72 C×30 s; 72 C×2 min)        -   Used the 50 nM primers reactions        -   Performed a first ExoSAP straight from product→failed to            remove all primers (Bioanalyzer): just leave this step out            in the future.        -   Dilute 1/10 (adding 90 ul H₂O)        -   Dilute 1/100→1/25 dilution=total 1/25′000        -   Probably did not perform ExoSAP clean up, small uncertainty            from notes    -   Append SQ tags (longer, full F-SQ and R-m.p. adaptor without        barcodes):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-m.p.; concentrations: 200            nM?        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×30 s, 65 C×15 s, 72            C×30 s; 72 C×2 min        -   Add 90 ul H2O, use 1 ul for next step, primer carry over            will be 1/100 of conc in this reaction    -   Barcoding PCR (p.9 quick book):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-BC1 to 12-lib.;            concentrations: 1 uM        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×15 s, 72 C×30 s; 72            C×2 min        -   Add 40 ul H₂O            →check 1 ul on Bioanalyzer DNA1000 chip→pool samples→clean            up→Bioanalyzer, adjust conc→sequencing            Prep of 1000-plex reactions            (Blue: 1000-plex; from amplified SQ libraries (p.32 lab book            BZ1))    -   BC2=ASQ8=pregnancy plasma 2666 or 2687; BC3=ASQ4=apo sup 16777    -   15 cycles STA        -   (RED STA protocol: 95 C×10 min; 95 C×15 s, 65 C×1 min, 60            C×4 min, 65 C×30 s, 72 C×30 s; 72 C×2 min)        -   50 nM target specific tagged R-primers and 200 nM            F-SQ-primer        -   Performed a first ExoSAP straight from product→failed to            remove all primers (Bioanalyzer): just leave this step out            in the future.        -   Dilute 1/5 (adding 40 ul H₂O)        -   2 ul in 14 ul ExoSAP reaction dilute to 100 ul=1/50 dilution            in this step=total 1/250    -   Append SQ tags (longer, full F-SQ and R-m.p. adaptor without        barcodes):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-m.p.; concentrations: 200            nM?        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×30 s, 65 C×15 s, 72            C×30 s; 72 C×2 min        -   Add 90 ul H2O, use 1 ul for next step, primer carry over            will be 1/100 of conc in this reaction    -   Barcoding PCR (p.9 quick book):        -   1 ul DNA in 10 ul PCR: F-SQ×R-SQ-BC1 to 12-lib.;            concentrations: 1 uM        -   15 cycles: 95 C×10 min; 95 C×15 s, 60 C×15 s, 72 C×30 s; 72            C×2 min        -   Add 40 ul H₂O            →check 1 ul on Bioanalyzer DNA1000 chip→pool samples→clean            up→Bioanalyzer, adjust conc→sequencing

Compositions of DNA

When performing an informatics analysis on sequencing data measured on amixture of fetal and maternal blood to determine genomic informationpertaining to the fetus, for example the ploidy state of the fetus, itmay be advantageous to measure the allele ratios at certain alleles.Unfortunately, in many cases, such as when attempting to determine theploidy state of a fetus from the DNA mixture found in the plasma of amaternal blood sample, the amount of DNA available is not sufficient todirectly measure the allele ratios in the mixture. In these cases,amplification of the DNA mixture will provide sufficient numbers of DNAmolecules that the desired allele ratios may be measured. However,current methods of amplification typically used in the amplification ofDNA for sequencing are often very biased, meaning that they do notamplify both alleles at a polymorphic locus by the same amount. A biasedamplification can result in allele ratios that are quite different fromthe allele ratios in the original mixture. Conventional methods do notuse statistical measurements of allele ratios at a large number ofpolymorphic loci. In contrast, in an embodiment of the presentdisclosure, amplification or enrichment methods that specifically enrichpolymorphic alleles and preserve allelic ratios is advantageous.

A number of methods are described herein that may be used topreferentially enrich a sample of DNA at a plurality of loci in a waythat minimizes allelic bias. Some examples are using circularizingprobes to target a plurality of loci where the 3′ ends and 5′ ends ofthe pre-circularized probe are designed to hybridize to bases that areone or a few positions away from the polymorphic regions of the targetedallele. Another is to use PCR probes where the 3′ end PCR probe isdesigned to hybridize to bases that are one or a few positions away fromthe polymorphic regions of the targeted allele. Another is to use asplit and pool approach to create mixtures of DNA where thepreferentially enriched loci are enriched with low allelic bias withoutthe drawbacks of direct multiplexing. Another is to use a hybrid captureapproach where the capture probes are designed such that the region ofthe capture probe that is designed to hybridize to the DNA flanking thepolymorphic region of the target is separated from the polymorphicregion by one or a small number of bases.

In the case where allelic ratio measurements at polymorphic loci areused to determine the ploidy state of an individual, it is desirable topreserve the ratio of alleles in a sample of DNA as it is prepared forgenetic measurements. This preparation may involve WGA amplification,targeted amplification, selective enrichment techniques, hybrid capturetechniques, circularizing probes or other methods meant to amplify theamount of DNA and/or selectively enhance the presence of molecules ofDNA that correspond to certain alleles.

In some embodiments of the present disclosure, there is a set of DNAprobes designed to target loci where the loci have maximal minor allelefrequencies. In some embodiments of the present disclosure, there is aset of probes that are designed to target where the loci have themaximum likelihood of the fetus having a highly informative SNP at thatloci. In some embodiments of the present disclosure, there is a set ofprobes that are designed to target loci where the probes are optimizedfor a given population subgroup. In some embodiments of the presentdisclosure, there is a set of probes that are designed to target lociwhere the probes are optimized for a given mix of population subgroups.In some embodiments of the present disclosure, there is a set of probesthat are designed to target loci where the probes are optimized for agiven pair of parents which are from different population subgroups thathave different minor allele frequency profiles. In some embodiments ofthe present disclosure, there is a circularized strand of DNA thatcontains at least one basepair that annealed to a piece of DNA that isof fetal origin. In some embodiments of the present disclosure, there isa circularized strand of DNA that contains at least one basepair thatannealed to a piece of DNA that is of placental origin. In someembodiments of the present disclosure, there is a circularized strand ofDNA that circularized while at least some of the nucleotides wereannealed to DNA that was of fetal origin. In some embodiments of thepresent disclosure, there is a circularized strand of DNA thatcircularized while at least some of the nucleotides were annealed to DNAthat was of placental origin. In some embodiments of the presentdisclosure, there is a set of probes wherein some of the probes targetsingle tandem repeats, and some of the probes target single nucleotidepolymorphisms. In some embodiments, the loci are selected for thepurpose of non-invasive prenatal diagnosis. In some embodiments, theprobes are used for the purpose of non-invasive prenatal diagnosis. Insome embodiments, the loci are targeted using a method that couldinclude circularizing probes, MIPs, capture by hybridization probes,probes on a SNP array, or combinations thereof. In some embodiments, theprobes are used as circularizing probes, MIPs, capture by hybridizationprobes, probes on a SNP array, or combinations thereof. In someembodiments, the loci are sequenced for the purpose of non-invasiveprenatal diagnosis.

In the case where the relative informativeness of a sequence is greaterwhen combined with relevant parent contexts, it follows that maximizingthe number of sequence reads that contain a SNP for which the parentalcontext is known may maximize the informativeness of the set ofsequencing reads on the mixed sample. In one embodiment the number ofsequence reads that contain a SNP for which the parent contexts areknown may be enhanced by using qPCR to preferentially amplify specificsequences. In one embodiment the number of sequence reads that contain aSNP for which the parent contexts are known may be enhanced by usingcircularizing probes (for example, MIPs) to preferentially amplifyspecific sequences. In one embodiment the number of sequence reads thatcontain a SNP for which the parent contexts are known may be enhanced byusing a capture by hybridization method (for example SURESELECT) topreferentially amplify specific sequences. Different methods may be usedto enhance the number of sequence reads that contain a SNP for which theparent contexts are known. In one embodiment of the present disclosure,the targeting may be accomplished by extension ligation, ligationwithout extension, capture by hybridization, or PCR.

In a sample of fragmented genomic DNA, a fraction of the DNA sequencesmap uniquely to individual chromosomes; other DNA sequences may be foundon different chromosomes. Note that DNA found in plasma, whethermaternal or fetal in origin is typically fragmented, often at lengthsunder 500 bp. In a typical genomic sample, roughly 3.3% of the mappablesequences will map to chromosome 13; 2.2% of the mappable sequences willmap to chromosome 18; 1.35% of the mappable sequences will map tochromosome 21; 4.5% of the mappable sequences will map to chromosome Xin a female; 2.25% of the mappable sequences will map to chromosome X(in a male); and 0.73% of the mappable sequences will map to chromosomeY (in a male). These are the chromosomes that are most likely to beaneuploid in a fetus. Also, among short sequences, approximately 1 in 20sequences will contain a SNP, using the SNPs contained on dbSNP. Theproportion may well be higher given that there may be many SNPs thathave not been discovered.

In one embodiment of the present disclosure, targeting methods may beused to enhance the fraction of DNA in a sample of DNA that map to agiven chromosome such that the fraction significantly exceeds thepercentages listed above that are typical for genomic samples. In oneembodiment of the present disclosure, targeting methods may be used toenhance the fraction of DNA in a sample of DNA such that the percentageof sequences that contain a SNP are significantly greater than what maybe found in typical for genomic samples. In one embodiment of thepresent disclosure, targeting methods may be used to target DNA from achromosome or from a set of SNPs in a mixture of maternal and fetal DNAfor the purposes of prenatal diagnosis.

Note that a method has been reported (U.S. Pat. No. 7,888,017) fordetermining fetal aneuploidy by counting the number of reads that map toa suspect chromosome and comparing it to the number of reads that map toa reference chromosome, and using the assumption that an over abundanceof reads on the suspect chromosome corresponds to a triploidy in thefetus at that chromosome. Those methods for prenatal diagnosis would notmake use of targeting of any sort, nor do they describe the use oftargeting for prenatal diagnosis.

By making use of targeting approaches in sequencing the mixed sample, itmay be possible to achieve a certain level of accuracy with fewersequence reads. The accuracy may refer to sensitivity, it may refer tospecificity, or it may refer to some combination thereof. The desiredlevel of accuracy may be between 90% and 95%; it may be between 95% and98%; it may be between 98% and 99%; it may be between 99% and 99.5%; itmay be between 99.5% and 99.9%; it may be between 99.9% and 99.99%; itmay be between 99.99% and 99.999%, it may be between 99.999% and 100%.Levels of accuracy above 95% may be referred to as high accuracy.

There are a number of published methods in the prior art thatdemonstrate how one may determine the ploidy state of a fetus from amixed sample of maternal and fetal DNA, for example: G. J. W. Liao etal. Clinical Chemistry 2011; 57(1) pp. 92-101. These methods targetthousands of locations along each chromosome. The number of locationsalong a chromosome that may be targeted while still resulting in a highaccuracy ploidy determination on a fetus, for a given number of sequencereads, from a mixed sample of DNA is unexpectedly low. In one embodimentof the present disclosure, an accurate ploidy determination may be madeby using targeted sequencing, using any method of targeting, for exampleqPCR, capture by hybridization, or circularizing probes, wherein thenumber of loci along a chromosome that need to be targeted may bebetween 1,000 and 500 loci; it may be between 500 and 300 loci; it maybe between 300 and 200 loci; it may be between 200 and 150 loci; it maybe between 150 and 100 loci; it may be between 100 and 50 loci; it maybe between 50 and 20 loci; it may be between 20 and 10 loci. Optimally,it may be between 100 and 500 loci. The high level of accuracy may beachieved by targeting a small number of loci and executing anunexpectedly small number of sequence reads. The number of reads may bebetween 5 million and 2 million reads; the number of reads may bebetween 2 million and 1 million; the number of reads may be between 1million and 500,000; the number of reads may be between 500,000 and200,000; the number of reads may be between 200,000 and 100,000; thenumber of reads may be between 100,000 and 50,000; the number of readsmay be between 50,000 and 20,000; the number of reads may be between20,000 and 10,000; the number of reads may be below 10,000.

In some embodiments, there is a composition comprising a mixture of DNAof fetal origin, and DNA of maternal origin, wherein the percent ofsequences that uniquely map to chromosome 13 is greater than 4%, greaterthan 5%, greater than 6%, greater than 7%, greater than 8%, greater than9%, greater than 10%, greater than 12%, greater than 15%, greater than20%, greater than 25%, or greater than 30%. In some embodiments of thepresent disclosure, there is a composition comprising a mixture of DNAof fetal origin, and DNA of maternal origin, wherein the percent ofsequences that uniquely map to chromosome 18 is greater than 3%, greaterthan 4%, greater than 5%, greater than 6%, greater than 7%, greater than8%, greater than 9%, greater than 10%, greater than 12%, greater than15%, greater than 20%, greater than 25%, or greater than 30%. In someembodiments of the present disclosure, there is a composition comprisinga mixture of DNA of fetal origin, and DNA of maternal origin, whereinthe percent of sequences that uniquely map to chromosome 21 is greaterthan 2%, greater than 3%, greater than 4%, greater than 5%, greater than6%, greater than 7%, greater than 8%, greater than 9%, greater than 10%,greater than 12%, greater than 15%, greater than 20%, greater than 25%,or greater than 30%. In some embodiments of the present disclosure,there is a composition comprising a mixture of DNA of fetal origin, andDNA of maternal origin, wherein the percent of sequences that uniquelymap to chromosome X is greater than 6%, greater than 7%, greater than8%, greater than 9%, greater than 10%, greater than 12%, greater than15%, greater than 20%, greater than 25%, or greater than 30%. In someembodiments of the present disclosure, there is a composition comprisinga mixture of DNA of fetal origin, and DNA of maternal origin, whereinthe percent of sequences that uniquely map to chromosome Y is greaterthan 1%, greater than 2%, greater than 3%, greater than 4%, greater than5%, greater than 6%, greater than 7%, greater than 8%, greater than 9%,greater than 10%, greater than 12%, greater than 15%, greater than 20%,greater than 25%, or greater than 30%.

In some embodiments, there is a composition comprising a mixture of DNAof fetal origin, and DNA of maternal origin, wherein the percent ofsequences that uniquely map to a chromosome, that contains at least onesingle nucleotide polymorphism is greater than 0.2%, greater than 0.3%,greater than 0.4%, greater than 0.5%, greater than 0.6%, greater than0.7%, greater than 0.8%, greater than 0.9%, greater than 1%, greaterthan 1.2%, greater than 1.4%, greater than 1.6%, greater than 1.8%,greater than 2%, greater than 2.5%, greater than 3%, greater than 4%,greater than 5%, greater than 6%, greater than 7%, greater than 8%,greater than 9%, greater than 10%, greater than 12%, greater than 15%,or greater than 20%, and where the chromosome is taken from the group13, 18, 21, X, or Y. In some embodiments of the present disclosure,there is a composition comprising a mixture of DNA of fetal origin, andDNA of maternal origin, wherein the percent of sequences that uniquelymap to a chromosome and that contain at least one single nucleotidepolymorphism from a set of single nucleotide polymorphisms is greaterthan 0.15%, greater than 0.2%, greater than 0.3%, greater than 0.4%,greater than 0.5%, greater than 0.6%, greater than 0.7%, greater than0.8%, greater than 0.9%, greater than 1%, greater than 1.2%, greaterthan 1.4%, greater than 1.6%, greater than 1.8%, greater than 2%,greater than 2.5%, greater than 3%, greater than 4%, greater than 5%,greater than 6%, greater than 7%, greater than 8%, greater than 9%,greater than 10%, greater than 12%, greater than 15%, or greater than20%, where the chromosome is taken from the set of chromosome 13, 18,21, X and Y, and where the number of single nucleotide polymorphisms inthe set of single nucleotide polymorphisms is between 1 and 10, between10 and 20, between 20 and 50, between 50 and 100, between 100 and 200,between 200 and 500, between 500 and 1,000, between 1,000 and 2,000,between 2,000 and 5,000, between 5,000 and 10,000, between 10,000 and20,000, between 20,000 and 50,000, and between 50,000 and 100,000.

In theory, each cycle in the amplification doubles the amount of DNApresent, however, in reality, the degree of amplification is slightlylower than two. In theory, amplification, including targetedamplification, will result in bias free amplification of a DNA mixture.When DNA is amplified, the degree of allelic bias typically increaseswith the number of amplification steps. In some embodiments, the methodsdescribed herein involve amplifying DNA with a low level of allelicbias. Since the allelic bias compounds, one can determine the per cycleallelic bias by calculating the nth root of the overall bias where n isthe base 2 logarithm of degree of enrichment. In some embodiments, thereis a composition comprising a second mixture of DNA, where the secondmixture of DNA has been preferentially enriched at a plurality ofpolymorphic loci from a first mixture of DNA where the degree ofenrichment is at least 10, at least 100, at least 1,000, at least10,000, at least 100,000 or at least 1,000,000, and where the ratio ofthe alleles in the second mixture of DNA at each locus differs from theratio of the alleles at that locus in the first mixture of DNA by afactor that is, on average, less than 1,000%, 500%, 200%, 100%, 50%,20%, 10%, 5%, 2%, 1%, 0.5%, 0.2%, 0.1%, 0.05%, 0.02%, or 0.01%. In someembodiments, there is a composition comprising a second mixture of DNA,where the second mixture of DNA has been preferentially enriched at aplurality of polymorphic loci from a first mixture of DNA where the percycle allelic bias for the plurality of polymorphic loci is, on average,less than 10%, 5%, 2%, 1%, 0.5%, 0.2%, 0.1%, 0.05%, or 0.02%. In someembodiments, the plurality of polymorphic loci comprises at least 10loci, at least 20 loci, at least 50 loci, at least 100 loci, at least200 loci, at least 500 loci, at least 1,000 loci, at least 2,000 loci,at least 5,000 loci, at least 10,000 loci, at least 20,000 loci, or atleast 50,000 loci.

Allele Distributions

In one embodiment, the goal of the method is to detect fetal copy numberbased on a maternal blood sample which contains some free-floating fetalDNA. In some embodiments, the fraction of fetal DNA compared to themother's DNA is unknown. The combination of a targeting method, such asLIPs, followed by sequencing results in a platform response thatconsists of the count of observed sequences associated with each alleleat each SNP. The set of possible alleles, either A/T or C/G, is known ateach SNP. Without loss of generality, the first allele will be labeled Aand the second allele will be labeled B. Thus, the measurement at eachSNP consists of the number of A sequences (N_(A)) and the number of Bsequences (N_(B)). These will be transformed for the purpose of futurecalculations into the total sequence count (n) and the ratio of Aalleles to total (r). The sequence count for a single SNP will bereferred to as the depth of read. The fundamental principal which allowscopy number identification from this data is that the ratio of A and Bsequences will reflect the ratio of A and B alleles present in the DNAbeing measured.

n=N _(A) +N _(B)

r=N _(A)/(N _(A) +N _(B))

Measurements will be initially aggregated over SNPs from the same parentcontext based on unordered parent genotypes. Each context is defined bythe mother genotype and the father genotype, for a total of 9 contexts.For example, all SNPs where the mother's genotype is AA and the father'sgenotype is BB are members of the AA|BB context. The A allele is definedas present at ratio r_(m) in the mother genotype and ratio r_(f) in thefather genotype. For example, the allele A is present at ratio r_(m)=1where the mother is AA and ratio r_(f)=0.5 where the father is AB. Thus,each context defines values for r_(m) and r_(f). Although the childgenotypes cannot always be predicted from the parent genotypes, theallele ratio averaged over a large number of SNPs can be predicted basedon the assumption that a parent AB genotype will contribute A and B atequal rates.

Consider a copy number hypothesis for the child of the form(n_(m),n_(f)) where n_(m) is the number of mother copies and n_(f) isthe number of father copies of the chromosome. The expected allele ratior_(c) in the child (averaged over SNPs in a particular parent context)depends on the allele ratios of the parent contexts and the parent copynumbers.

$\begin{matrix}{r_{c} = \frac{{n_{m}r_{m}} + {n_{f}r_{f}}}{n_{m} + n_{f}}} & (1)\end{matrix}$

In a mixture of maternal and fetal blood, allele copies will becontributed from both the mother directly and from the child. Assumethat the fraction of child DNA present in the mixture is δ. Then in themixture, the ratio r of the A allele in a given context is a linearcombination of the mother ratio r_(m) and the child ratio r_(c), whichcan be reduced to a linear combination of the mother ratio and fatherratio using equation 1.

$\begin{matrix}\begin{matrix}{r = {{\left( {1 - \delta} \right)r_{m}} + {\delta \; r_{c}}}} \\{= {{\left( {1 - \frac{\delta \; n_{f}}{n_{m} + n_{f}}} \right)r_{m}} + {\frac{\delta \; n_{f}}{n_{m} + n_{f}}r_{f}}}}\end{matrix} & (2)\end{matrix}$

Equation 2 predicts the expected ratio of A alleles for SNPs in a givencontext as a function of the copy number hypothesis (n_(m),n_(f)). Notethat the allele ratio on individual SNPs is not predicted by thisequation because these depend on random assignment where at least oneparent is heterozygous. Therefore, the set of sequences from all SNPs ina particular context will be combined. Assuming that the contextcontains m SNPs, and recalling that n sequences will be produced fromeach SNP, the data from that context consists of N=mn sequences. Each ofthe N sequences is considered an independent random trial where thetheoretical rate of A sequences is the allele ratio r. The measured rateof A sequences r is therefore known to be Gaussian distributed with meanr and variance δ²=r(1−r)/N.

Recall that the theoretical allele ratio is a function of the parentcopy numbers (n_(m),n_(f)). Thus, each hypothesis h results in apredicted allele ratio r_(i) ^(h) for the SNP in parent context i. Thedata likelihood is defined as the probability of a given hypothesisproducing the observed data. Thus, the likelihood of measurement r_(i)^(h) from context i under hypothesis h is a binomial distribution, whichcan be approximated for large N as a Gaussian distribution with thefollowing mean and variance. The mean is determined by the context andthe hypothesis as described in equation 2.

p(r̂_(i)|h) = (r̂_(i); μ, σ) μ = r_(i)^(h)$\sigma = \sqrt{\frac{r_{i}^{h}\left( {1 - r_{i}^{h}} \right)}{N_{i}}}$

The measurements on each of the nine contexts are assumed independentgiven the parent copy numbers, due to the common assumption ofindependent noise on each SNP. Thus, the data from a particularchromosome consists of the sequence measurements from contexts i rangingfrom 1 to 9. The likelihood of the observed allele ratios {{circumflexover (r)}₁ . . . , {circumflex over (r)}₉} from the whole chromosome istherefore the product of the individual context likelihoods:

$\begin{matrix}{{p\left( {{{\hat{r}}_{1}\mspace{14mu} \ldots}\mspace{14mu},{\hat{r}}_{9}} \right)} = {\prod\limits_{i = 1}^{9}\; {p\left( {\hat{r}}_{i} \middle| h \right)}}} \\{= {\prod\limits_{i = 1}^{9}\; {\left( {{{\hat{r}}_{i};r_{i}^{h}},\sqrt{\frac{r_{i}^{h}\left( {1 - r_{i}^{h}} \right)}{N_{i}}}} \right)}}}\end{matrix}$

Parameter Estimation

Equation 2 predicts the allele ratio as a function of parent copy numberhypothesis, but also includes the fraction of child DNA. Therefore, thedata likelihood for each chromosome is a function of through its effecton r_(i) ^(h). This effect is highlighted through the notationp({circumflex over (r)}₁ . . . , {circumflex over (r)}₉|h; δ). Thisparameter cannot be predicted with high accuracy, and therefore must beestimated from the data. A number of different approaches may be usedfor parameter estimation. One method involves the measurement ofchromosomes for which copy number errors are not viable at the stage ofdevelopment where testing will be performed. The other method measuresonly chromosomes on which errors are expected to occur.

Measure Some Chromosomes Known to be Disomy

In this method, certain chromosomes will be measured which cannot havecopy number errors at the state of development when testing isperformed. These chromosomes will be referred to as the training set T.The copy number hypothesis on these chromosomes is (1,1). Assuming thateach chromosome is independent, the data likelihood of the measurementsfrom all chromosomes t in T is the product of the individual chromosomelikelihoods. The child fraction δ can be selected to maximize the datalikelihood across the chromosomes in T conditioned on the disomyhypothesis. Let R_(t) represent the set of measurements {circumflex over(r)}_(i) from all contexts i on chromosome t. Then, the maximumlikelihood estimate δ* solves the following:

δ*=argmin_(δ)Π_(tεT) p(R _(t) |h=(1,1);δ)

This optimization has only one degree of freedom constrained betweenzero and one, and therefore can easily be solved using a variety ofnumerical methods. The solution δ* can then be substituted into equation2 in order to calculate the likelihoods of each hypothesis on eachchromosome.

Measure Only Chromosomes which May have Copy Number Errors

If copy number errors are possible on all of the chromosomes beingmeasured, the child concentration must be estimated in parallel with thecopy number hypotheses. Note that the same copy number error present onall measured chromosomes will be very difficult to detect. For example,maternal trisomy on all chromosomes at a given child concentration willresult in the same theoretical allele ratios as disomy on allchromosomes at lower child concentration, because in both cases thecontribution of mother alleles compared to father alleles increasesuniformly across all chromosomes and contexts.

A straight forward approach for classification of a limited set ofchromosomes t is to consider the joint chromosome hypothesis H, whichconsists of the joint set of hypotheses for all chromosomes beingtested. If the chromosome hypotheses consist of disomy, maternal trisomyand paternal trisomy, the number of possible joint hypotheses is 3^(T)where T is the number of tested chromosomes. A maximum likelihoodestimate δ*(H) can be calculated conditioned on each joint hypothesis.The likelihood of the joint hypothesis is thus calculated as follows:

δ*(H)=argmax_(δ)Π_(t=1) ^(T) p(R _(t) |H;δ)

p(all data|H)=Π_(t=1) ^(T) p(R _(t) |H;δ*(H))

The joint hypothesis likelihoods p(all data|H) can be calculated foreach joint hypothesis H, and the maximum likelihood hypothesis isselected, with its corresponding estimate δ*(H) of the child fraction.

Performance Specifications

The ability to distinguish between parent copy number hypotheses isdetermined by models discussed in the previous section. At the mostgeneral level, the difference in expected allele ratios under thedifferent hypotheses must be large compared to the standard deviationsof the measurements. Consider the example of distinguishing betweendisomy and maternal trisomy, or hypotheses h₁=(1,1) and h₂=(2,1).Hypothesis 1 predicts allele ratio r¹ and hypothesis 2 predictionsallele ratio r², as a function of the mother allele ratio r_(m) andfather allele ratio r_(f) for the context under consideration.

$r^{1} = {{\left( {1 - \frac{\delta}{2}} \right)r_{m}} + {\frac{\delta}{2}r_{f}}}$$r^{2} = {{\left( {1 - \frac{\delta}{3}} \right)r_{m}} + {\frac{\delta}{3}r_{f}}}$

The measured allele ratio {circumflex over (r)} is predicted to beGaussian distributed, either with mean r¹ or mean r², depending onwhether hypothesis 1 or 2 is true. The standard deviation of themeasured allele ratio depends similarly on the hypothesis, according toequation 3. In a scenario where one can expect to identify eitherhypothesis 1 or 2 as truth based on the measurement r, the means r¹, r²and standard deviations σ¹, σ² must satisfy a relationship such as thefollowing, which guarantees that the means are far apart compared to thestandard deviations. This criterion represents a 2 percent error rate,meaning a 2 percent chance of either false negative or false positive.

|r ¹ −r ²|>2σ¹+2σ²

Substituting the copy numbers for disomy (1, 1) and maternal trisomy(2, 1) for hypotheses 1 and 2 results in the following condition:

${{\frac{\delta}{6}\left( {r_{f} - r_{m}} \right)}} > {2\sigma_{1}^{+}2\sigma_{2}}$$\sigma^{1} = \sqrt{\frac{r_{1}\left( {1 - r^{1}} \right)}{N}}$$\sigma^{2} = \sqrt{\frac{r_{2}\left( {1 - r^{2}} \right)}{N}}$$\sigma^{2} = \sqrt{\frac{r_{2}\left( {1 - r^{2}} \right)}{N}}$

FIG. 1 shows the required number of measurements (number of SNPsmultiplied by depth of read) versus child concentration required tosatisfy the previous condition. Two different parent contexts are shown.In practice, measurements from multiple contexts may be combined,resulting in a smaller number of required measurements per context.

Overview of the Analysis Method

In one embodiment of the present disclosure, using the parent contexts,and chromosomes known to be euploid, it is possible to estimate, by aset of simultaneous equations, the proportion of DNA in the maternalblood from the mother and the proportion of DNA in the maternal bloodfrom the fetus. These simultaneous equations are made possible by theknowledge of the alleles present on the father. In particular, allelespresent on the father and not present on the mother provide a directmeasurement of fetal DNA. One may then look at the particularchromosomes of interest, such as chromosome 21, and see whether themeasurements on this chromosome under each parental context areconsistent with a particular hypothesis, such as H_(mp) where mrepresents the number of maternal chromosomes and p represents thenumber of paternal chromosomes e.g. H₁₁ representing euploid, H₂₁ andH₁₂ representing maternal and paternal trisomy respectively.

It is important to note that this method does not use a referencechromosome as a basis by which to compare observed allelic ratios on thechromosome of interest.

This disclosure presents a method by which one may determine the ploidystate of a gestating fetus, at one or more chromosome, in a non-invasivemanner, using genetic information determined from fetal DNA found inmaternal blood. The fetal DNA may be purified, partially purified, ornot purified; genetic measurements may be made on DNA that originatedfrom more than one individual. Informatics type methods can infergenetic information of the target individual, such as the ploidy state,from the bulk genotypic measurements at a set of alleles. The set ofalleles may contain various subsets of alleles, wherein one or moresubsets may correspond to alleles that are found on the targetindividual but not found on the non-target individuals, and one or moreother subsets may correspond to alleles that are found on the non-targetindividual and are not found on the target individual. The method mayinvolve using comparing ratios of measured output intensities forvarious subsets of alleles to expected ratios given various potentialploidy states. The platform response may be determined, and a correctionfor the bias of the system may be incorporated into the method.

Key Assumptions of the Method:

-   -   The expected amount of genetic material in the maternal blood        from the mother is constant across all loci.    -   The expected amount of genetic material present in the maternal        blood from the fetus is constant across all loci assuming the        chromosomes are euploid.    -   The chromosomes that are non-viable (all excluding 13,18,21,X,Y)        are all euploid in the fetus. In one embodiment, only some of        the non-viable chromosomes need be euploid on the fetus.

General Problem Formulation:

One may write y_(ijk)=g_(ijk)(x_(ijk))+v_(ijk) where x_(ijk) is thequantity of DNA on the allele k=1 or 2 (1 represents allele A and 2represents allele B), j=1 . . . 23 denotes chromosome number and i=1 . .. N denotes the locus number on the chromosome, g_(ijk) is platformresponse for particular locus and allele ijk, and v_(ijk) is independentnoise on the measurement for that locus and allele. The amount ofgenetic material is given by x_(ijk)=am_(ijk)+Δc_(ijk) where a is theamplification factor (or net effect of leakage, diffusion, amplificationetc.) of the genetic material present on each of the maternalchromosomes, m_(ijk) (either 0,1,2) is the copy number of the particularallele on the maternal chromosomes, Δ is the amplification factor of thegenetic material present on each of the child chromosomes, and c_(ijk)is the copy number (either 0,1,2,3) of the particular allele on thechild chromosomes. Note that for the first simplified explanation, a andΔ are assumed to be independent of locus and allele i.e. independent ofi, j, and k. This gives:

y _(ijk) =g _(ijk)(am _(ijk) +Δc _(ijk))+v _(ijk)

Approach Using an Affine Model that is Uniform Across All Loci:

One may model g with an affine model, and for simplicity assume that themodel is the same for each locus and allele, although it will beunderstood after reading this disclosure how to modify the approach whenthe affine model is dependent on i,j,k. Assume the platform responsemodel is

g _(ijk)(x _(ijk))=b+am _(ijk) +Δc _(ijk)

where amplification factors a and Δ have been used without loss ofgenerality, and a y-axis intercept b has been added which defines thenoise level when there is no genetic material. The goal is to estimate aand Δ. It is also possible to estimate b independently, but assume fornow that the noise level is roughly constant across loci, and only usethe set of equations based on parent contexts to estimate a and Δ. Themeasurement at each locus is given by

y _(ijk) =b+am _(ijk) +Δc _(ijk) +v _(ijk)

Assuming that the noise v_(ijk) is i.i.d. for each of the measurementswithin a particular parent context, T, one can sum the signals withinthat parent context. The parent contexts are represented in terms ofalleles A and B, where the first two alleles represent the mother andthe second two alleles represent the father: Tε{AA|BB, BB|AA, AB|AB,AA|AA, BB|BB, AA|AB, AB|AA, AB|BB}. For each context T, there is a setof loci i,j where the parent DNA conforms to that context, representedi,jεT. Hence:

$y_{T,k} = {{\frac{1}{N_{T}}{\sum\limits_{i,{j \in T}}y_{i,j,k}}} = {b + {a\overset{\_}{m_{k,T}}} + {\Delta \overset{\_}{c_{k,T}}} + \overset{\_}{v_{k,T}}}}$

Where m_(k,T) , c_(k,T) and v_(k,T) represent the means of therespective values over all the loci conforming to the parent context T,or over all i,jεT. The mean or expected values c_(k,T) will depend onthe ploidy status of the child. The table below describes the mean orexpected values m_(k,T) and c_(k,T) for k=1(allele A) or 2(allele B) andall the parent contexts T. One may calculate the expected valuesassuming different hypotheses on the child, namely euploidy and maternaltrisomy. The hypotheses are denoted by the notation H_(mf), where mrefers to the number of chromosomes from the mother and f refers to thenumber of chromosomes from the father e.g. H₁₁ is euploid, H₂₁ ismaternal trisomy. Note that there is symmetry between some of the statesby switching A and B, but all states are included for clarity:

Context AA/BB BB/AA AB/AB AA/AA BB/BB AA/AB AB/AA AB/BB BB/AB m_(A,T) 20 1 2 0 2 1 1 0 m_(B,T) 0 2 1 0 2 0 1 1 2 c_(A,T) |H₁₁ 1 1 1 2 0 1.5 1.50.5 0.5 c_(B,T) |H₁₁ 1 1 1 0 2 0.5 0.5 1.5 1.5 c_(A,T) |H₂₁ 2 1 1.5 3 02.5 2 1 0.5 c_(B,T) |H₂₁ 1 2 1.5 0 3 0.5 1 2 2.5It is now possible to write a set of equations describing all theexpected values y_(T,k), which can be cast in matrix form, as follows:

Y=B+A _(H) P+v

Where

Y=[y _(AA|BB,1) y _(BB|AA,1) y _(AB|BB,1) y _(AA|AA,1) y _(BB|BB,1) y_(AA|AB,1) y _(AB|AA,1) y _(AB|BB,1) y _(BB|AB,1) y _(AA|BB,2) y_(BB|AA,2) y _(AB|AB,2) y _(AA|AA,2) y _(BB|BB,2) y _(AA|AB,2) y_(AB|AA,2) y _(AB|BB,2) y _(BB|AB,2)]^(T)

P=[_(Δ) ^(a)] is the matrix of parameters to estimateB=b{right arrow over (1)} where {right arrow over (1)} is the 18×1matrix of onesv=[ v_(A,AA|BB) . . . v_(B,BB|AB) ]^(T) is the 18×1 matrix of noisetermsand A_(H) is the matrix encapsulating the data in the table, where thevalues are different for each hypothesis H on the ploidy state of thechild. Below are examples of the Matrix A_(H) for the ploidy hyopothesesH₁₁ and H₂₁

$A_{H_{11}} = {{\begin{bmatrix}2.0 & 1.0 \\0 & 1.0 \\1.0 & 1.0 \\2.0 & 2.0 \\0 & 0 \\2.0 & 1.5 \\1.0 & 1.5 \\1.0 & 0.5 \\0 & 0.5 \\0 & 1.0 \\2.0 & 1.0 \\1.0 & 1.0 \\0 & 0 \\2.0 & 2.0 \\0 & 0.5 \\1.0 & 0.5 \\1.0 & 1.5 \\2.0 & 1.5\end{bmatrix}\mspace{14mu} A_{H_{21}}} = \begin{bmatrix}2.0 & 2.0 \\0 & 1.0 \\1.0 & 1.5 \\2.0 & 3.0 \\0 & 0 \\2.0 & 2.5 \\1.0 & 2.0 \\1.0 & 1.0 \\0 & 0.5 \\0 & 1.0 \\2.0 & 2.0 \\1.0 & 1.5 \\0 & 0 \\2.0 & 3.0 \\0 & 0.5 \\1.0 & 1.0 \\1.0 & 2.0 \\2.0 & 2.5\end{bmatrix}}$

In order to estimate a and Δ, or matrix P, aggregate the data across aset of chromosomes that one may assume are euploid on the child sample.This could include all chromosomes j=1 . . . 23 except those that areunder test, namely j=13, 18, 21, X and Y. (Note: one could also apply aconcordance test for the results on the individual chromosomes in orderto detect mosaic aneuploidy on the non-viable chromosomes.) In order toclarify notation, define Y′ as Y measured over all the euploidchromosomes, and Y″ as Y measured over a particular chromosome undertest, such as chromosome 21, which may be aneuploid. Apply the matrixA_(H) ₁₁ to the euploid data in order to estimate the parameters:

{circumflex over (P)}=argmin_(p) ∥Y′−B−A _(H) ₁₁ P∥ ₂=(A _(H) ₁₁ ^(T) A_(H) ₁₁ )⁻¹ A _(H) ₁₁ ^(T) {tilde over (Y)}

where {tilde over (Y)}=Y′−B, i.e., the measured data with the biasremoved. The least-squares solution above is only the maximum-likelihoodsolution if each of the terms in the noise matrix v has a similarvariance. This is not the case, most simply because the number of lociN′_(T) used to compute the mean measurement for each context T isdifferent for each context. As above, use the N_(T)′ to refer to thenumber of loci used on the chromosomes known to be euploid, and use theC′ to denote the covariance matrix for mean measurements on thechromosomes known to be euploid. There are many approaches to estimatingthe covariance C′ of the noise matrix v, which one may assume isdistributed as v˜N(0,C′). Given the covariance matrix, themaximum-likelihood estimate of P is

{circumflex over (P)}=argmin_(p) ∥C′ ^(−1/2)(Y′−B−A _(H) ₁₁ P)∥₂=(A _(H)₁₁ ^(T) C′ ⁻¹ A _(H) ₁₁ )⁻¹ A _(H) ₁₁ ^(T) C′ ⁻¹ {tilde over (Y)}

One simple approach to estimating the covariance matrix is to assumethat all the terms of v are independent (i.e. no off-diagonal terms) andinvoke the Central Limit Theorem so that the variance of each term of vscales as 1/N′_(T) so that one may find the 18×18 matrix

$C^{\prime} = \begin{bmatrix}{1/N_{{AA}{BB}}^{\prime}} & \ldots & 0 \\\vdots & \ddots & \vdots \\0 & \ldots & {1/N_{{BB}{AB}}^{\prime}}\end{bmatrix}$

Once P′ has been estimated, use these parameters to determine the mostlikely hypothesis on the chromosome under study, such as chromosome 21.In other words, choose the hypothesis:

H*=argmin_(H) ∥C″ ^(−1/2)(Y″−B−A _(H) {circumflex over (P)})∥₂

Having found H* one may then estimate the degree of confidence that onemay have in the determination of H*. Assume, for example, that there aretwo hypotheses under consideration: H₁₁ (euploid) and H₂₁ (maternaltrisomy). Assume that H*=H₁₁. Compute the distance measurescorresponding to each of the hypotheses:

d ₁₁ =∥C″ ^(−1/2)(Y″−B−A _(H) ₁₁ {circumflex over (P)})∥₂

d ₂₁ =∥C″ ^(−1/2)(Y″−B−A _(H) ₂₁ {circumflex over (P)})∥₂

It can be shown that the square of these distance measures are roughlydistributed as a Chi-Squared random variable with 18 degrees of freedom.Let χ₁₈ represent the corresponding probability density function forsuch a variable. One may then find the ratio in the probabilities p_(H)of each of the hypotheses according to:

$\frac{p_{H_{11}}}{p_{H_{21}}} = \frac{\chi_{18{(d_{11}^{2})}}}{\chi_{18{(d_{21}^{2})}}}$

One may then compute the probabilities of each hypothesis by adding theequation p_(H) ₁₁ +p_(H) ₂₁ =1. The confidence that the chromosome is infact euploid is given by p_(H) ₁₁ .

Variations on the Method

(1) One may modify the above approach for different biases b on each ofthe channels representing alleles A and B. The bias matrix B isredefined as follows:

$B = \begin{bmatrix}{b_{A}\overset{->}{1}} \\{b_{B}\overset{->}{1}}\end{bmatrix}$

where {right arrow over (1)} is a 9×1 matrix of ones. As discussedabove, the parameters b_(e) and b_(ib) can either be assumed based ona-priori measurements, or can be included in the matrix P and activelyestimated (i.e. there is sufficient rank in the equations over all thecontexts to do so).

(2) In the general formulation, wherey_(ijk)=g_(ijk)(am_(ijk)+Δc_(ijk))+v_(ijk), one may directly measure orcalibrate the function g_(ijk) for every locus and allele, so that thefunction (which one may assume is monotonic for the vast majority ofgenotyping platforms) can be inverted. One may then use the functioninverse to recast the measurements in terms of the quantity of geneticmaterial so that the system of equations is linear i.e. y′_(ijk)=g_(ijk)⁻¹(y_(ijk))=am_(ijk)+Δc_(ijk)+v′_(ijk). This approach is particularlygood when g_(ijk) is an affine function so that the inversion does notproduce amplification or biasing of the noise in v′_(ijk).

(3) The method above may not be optimal from a noise perspective sincethe modified noise term v′_(ijk)=g_(ijk) ⁻¹(v_(ijk)) may be amplified orbiased by the function inversion. Another approach is to linearism themeasurements around an operating point i.e.y_(ijk)=g_(ijk)(am_(ijk)+Δc_(ijk))+v_(ijk) may be recast as:y_(ijk)≈g_(ijk)(am_(ijk))+g_(ijk)′(am_(ijk))Δc_(ijk)+v_(ijk). Since onemay expect no more than 30% of the free-floating DNA in the maternalblood to be from the child, Δ<<a, and the expansion is a reasonableapproximation. Alternatively, for a platform response such as that ofthe ILLUMINA BEAD ARRAY, which is monotonically increasing and for whichthe second derivative is always negative, one could improve thelinearization estimate according to y_(ijk)≈g_(ijk)(am_(ijk))+0.5(g_(ijk)′(am_(ijk))+g_(ijk)′(am_(ijk)+Δc_(ijk)))Δc_(ijk)+v_(ijk).The resulting set of equations may be solved iteratively for a and Δusing a method such as Newton-Raphson optimization.

(4) Another general approach is to measure at the total amount of DNA onthe test chromosome (mother plus fetus) and compare with the amount ofDNA on all other chromosomes, based on the assumption that amount of DNAshould be constant across all chromosomes. Although this is simpler, onedisadvantage is that it is now known how much is contributed by thechild so it is not possible to estimate confidence bounds meaningfully.However, one could look at standard deviation across other chromosomesignals that should be euploid to estimate the signal variance andgenerate a confidence bound. This method involves including measurementsof maternal DNA which are not on the child DNA so these measurementscontribute nothing to the signal but do contribute directly to noise. Inaddition, it is not possible to calibrate out the amplification biasesamongst different chromosomes. To address this last point, it ispossible to find a regression function linking each chromosome's meansignal level to every other chromosomes mean signal level, combine thesignal from all chromosome by weighting based on variance of theregression fit, and look to see whether the test chromosome of interestis within the acceptable range as defined by the other chromosomes.

(5) This method may be used in conjunction with other method previouslydisclosed by Gene Security Network, especially those method that arepart of PARENTAL SUPPORT™, such that one may phase the parents so thatit is known what is contained on each individual maternal and paternalchromosome. By considering the odds ratio of each of the alleles atheterozygous loci, one may determine which haplotype of the mother ispresent on the child. Then one can compare the signal level of themeasurable maternal haplotype to the paternal haplotype that is present(without background noise from the mother) and see when that ratio of1:1 is not satisfied due to aneuploidy which causes an imbalance betweenmaternal and paternal alleles.

This list of possible variations on the method is not meant to beexhaustive. Other variation may also be employed.

Maximum Likelihood Model Using Percent Fetal Fraction

Determining the ploidy status of a fetus by measuring the free floatingDNA contained in maternal serum, or by measuring the genotypic datacontained in any mixed sample, is a non-trivial exercise. There are anumber of methods, for example, performing a read count analysis wherethe presumption is that if the fetus is trisomic at a particularchromosome, then the overall amount of DNA from that chromosome found inthe maternal blood will be elevated with respect to a referencechromosome. One way to detect trisomy in such fetuses is to normalizethe amount of DNA expected for each chromosome, for example, accordingto the number of SNPs in the analysis set that correspond to a givenchromosome, or according to the number of uniquely mappable portions ofthe chromosome. Once the measurements have been normalized, anychromosomes for which the amount of DNA measured exceeds a certainthreshold are determined to be trisomic. This approach is described inFan, et al. PNAS, 2008; 105(42); pp. 16266-16271, and also in Chiu etal. BMJ 2011; 342:c7401. In the Chiu et al. paper, the normalization wasaccomplished by calculating a Z score as follows:

Z score for percentage chromosome 21 in test case=((percentagechromosome 21 in test case)−(mean percentage chromosome 21 in referencecontrols))/(standard deviation of percentage chromosome 21 in referencecontrols).

These methods determine the ploidy status of the fetus using a singlehypothesis rejection method. However, they suffer from some significantshortcomings. Since these methods for determining ploidy in the fetusare invariant according to the percentage of fetal DNA in the sample,they use one cut off value; the result of this is that the accuracies ofthe determinations are not optimal, and those cases where the percentageof fetal DNA in the mixture are relatively low will suffer the worstaccuracies.

In one embodiment of the present disclosure, the method used todetermine the ploidy state of the fetus involves taking into account thefraction of fetal DNA in the sample. In another embodiment of thepresent disclosure, the method involves the use of maximum likelihoodestimations. In one embodiment of the present disclosure, the methodinvolves calculating the percent of DNA in a sample that is fetal orplacental in origin. In one embodiment of the present disclosure, thethreshold for calling aneuploidy is adaptively adjusted based on thecalculated percent fetal DNA. In some embodiments, the method forestimating the percentage of DNA that is of fetal origin in a mixture ofDNA, comprises obtaining a mixed sample that contains genetic materialfrom the mother, and genetic material from the fetus, obtaining agenetic sample from the father of the fetus, measuring the DNA in themixed sample, measuring the DNA in the father sample, and calculatingthe percentage of DNA that is of fetal origin in the mixed sample usingthe DNA measurements of the mixed sample, and of the father sample.

In one embodiment of the present disclosure, the fraction of fetal DNA,or the percentage of fetal DNA in the mixture can be measured. In someembodiments the fraction can be calculated using only the genotypingmeasurements made on the maternal plasma sample itself, which is amixture of fetal and maternal DNA. In some embodiments the fraction maybe calculated also using the measured or otherwise known genotype of themother and/or the measured or otherwise known genotype of the father. Insome embodiments the percent fetal DNA may be calculated using themeasurements made on the mixture of maternal and fetal DNA along withthe knowledge of the parental contexts. In one embodiment the fractionof fetal DNA may be calculated using population frequencies to adjustthe model on the probability on particular allele measurements.

In one embodiment of the present disclosure, a confidence may becalculated on the accuracy of the determination of the ploidy state ofthe fetus. In one embodiment, the confidence of the hypothesis ofgreatest likelihood (H_(major)) may be calculated as (1−H_(major))/Σ(allH). It is possible to determine the confidence of a hypothesis if thedistributions of all of the hypotheses are known. It is possible todetermine the distribution of all of the hypotheses if the parentalgenotype information is known. It is possible to calculate a confidenceof the ploidy determination if the knowledge of the expecteddistribution of data for the euploid fetus and the expected distributionof data for the aneuploid fetus are known. It is possible to calculatethese expected distributions if the parental genotype data are known. Inone embodiment one may use the knowledge of the distribution of a teststatistic around a normal hypothesis and around an abnormal hypothesisto determine both the reliability of the call as well as refine thethreshold to make a more reliable call. This is particularly useful whenthe amount and/or percent of fetal DNA in the mixture is low. It willhelp to avoid the situation where a fetus that is actually aneuploid isfound to be euploid because a test statistic, such as the Z statisticdoes not exceed a threshold that is made based on a threshold that isoptimized for the case where there is a higher percent fetal DNA.

Ploidy Calling for a Mother/Child Mixture

Described herein is a method for determining the ploidy state of a fetusgiven sequence data that was measured on free floating DNA isolated frommaternal blood, wherein the free floating DNA contains some DNA ofmaternal origin, and some DNA of fetal/placental origin. This sectionwill describe one embodiment of the present disclosure in which theploidy state of the fetus is determined using the calculated fraction offetal DNA in the mixture that has been analyzed. It will also describean embodiment in which the fraction of fetal DNA or the percentage offetal DNA in the mixture can be measured. In some embodiments thefraction can be calculated using only the genotyping measurements madeon the maternal blood sample itself, which is a mixture of fetal andmaternal DNA. In some embodiments the fraction may be calculated alsousing the measured or otherwise known genotype of the mother and/or themeasured or otherwise known genotype of the father.

For a particular chromosome, suppose there are N SNPs, for which:

-   -   Parent genotypes from ILLUMINA data, assumed to be correct:        mother m=(m₁, . . . , m_(N)), father f=(f₁, . . . , f_(N)),        where m_(i), f_(i)ε(AA,AB, BB).    -   Set of NR sequence measurements S=(s₁, . . . , s_(nr)).        Deriving Most Likely Copy Number from Data

For each copy number hypothesis H considered, derive data log likelihoodLIK(H) on a whole chromosome and choose the best hypothesis maximizingLIK, i.e.

$H^{*} = {\underset{H}{argmax}L\; I\; {K(H)}}$

Copy Number Hypotheses Considered are:

-   -   Monosomy:        -   maternal H10(one copy from mother)        -   paternal H01(one copy from father)    -   Disomy: H11(one copy each mother and father)    -   Simple trisomy, no crossovers considered:        -   Maternal: H21_matched (two identical copies from mother, one            copy from father), H21_unmatched (BOTH copies from mother,            one copy from father)        -   Paternal: H12_matched (one copy from mother, two identical            copies from father), H12_unmatched (one copy from mother,            both copies from father)    -   Composite trisomy, allowing for crossovers (using a joint        distribution model):        -   maternal H21 (two copies from mother, one from father),        -   paternal H12 (one copy from mother, two copies from father)            If there were no crossovers, each trisomy, whether the            origin was mitotis, meiosis I, or meiosis II, would be one            of the matched or unmatched trisomies. Due to crossovers,            true trisomy is a combination of the two. First, a method to            derive hypothesis likelihoods for simple hypotheses is            described. Then a method to derive hypothesis likelihoods            for composite hypotheses is described, combining individual            SNP likelihood with crossovers.

LIK(H) for Simple Hypotheses

For simple hypotheses H, LIK(H), the log likelihood of hypothesis H on awhole chromosome, is calculated as the sum of log likelihoods ofindividual SNPs, i.e.

${L\; I\; {K(H)}} = {\sum\limits_{i}{L\; I\; {K\left( {i,H} \right)}}}$

This hypothesis does not assume any linkage between SNPs, and thereforedoes not utilize a joint distribution model.

Log Likelihood Per SNP

On a particular SNP i, define m_(i)=true mother genotype, f_(i)=truefather genotype, cf=known or derived child fraction. Let x_(i)=P(A|i,S)be the probability of having an A on SNP i, given the sequencemeasurements S. Assuming child hypothesis H, log likelihood of observeddata on SNP i is defined as

$\begin{matrix}{{L\; I\; {K\left( {i,H} \right)}} = {\log \; {{lik}\left( {{x_{i}m_{i}},f_{i},H,{cf}} \right)}}} \\{= {\sum\limits_{c}{{p\left( {{cm_{i}},f_{i},H} \right)}*\log \; {{lik}\left( {{x_{i}m_{i}},c,{cf}} \right)}}}}\end{matrix}$

p(c|m,f,H) is the probability of getting true child genotype=c, givenparents m, f, and assuming hypothesis H, which can be easily calculated.For example, for H11, H21 matched and H21 unmatched, p(c|m,f,H) is givenbelow.

p(c|m,f,H) H11 H21 matched H21 unmatched m f AA AB BB AAA AAB ABB BBBAAA AAB ABB BBB AA AA 1 0 0 1 0 0 0 1 0 0 0 AB AA 0.5 0.5 0 0.5 0 0.5 00 1 0 0 BB AA 0 1 0 0 0 1 0 0 0 1 0 AA AB 0.5 0.5 0 0.5 0.5 0 0 0.5 0.50 0 AB AB 0.25 0.5 0.25 0.25 0.25 0.25 0.25 0 0.5 0.5 0 BB AB 0 0.5 0.50 0 0.5 0.5 0 0 0.5 0.5 AA BB 0 1 0 0 1 0 0 0 1 0 0 AB BB 0 0.5 0.5 00.5 0 0.5 0 0 1 0 BB BB 0 0 1 0 0 0 1 0 0 0 1

lik(x_(i)|m,c,cf) is the likelihood of getting derived probability x_(i)on SNP i, assuming true mother m, true child c, defined aspdf_(X)(x_(i)) of the distribution that x_(i) should be following ifhypothesis H were true. In particular lik(x_(i)|m,c,cf)=pdf_(X)(x_(i))

In a simple case where Di of NR sequences in S line up to SNP i,X˜(1/D_(i))Bin(p,D_(i)), where p=p(A|m,c,cf)=probability of getting anA, for this mother/child mixture, calculated as:

${p\left( {{Am},c,{cf}} \right)} = \frac{{\# {A(m)}*\left( {1 - {cf}_{correct}} \right)} + {\# {A(c)}*{cf}_{correct}}}{{n_{m}*\left( {1 - {cf}_{correct}} \right)} + {n_{c}*{cf}_{correct}}}$

where #A(g)=number of A's in genotype g, =2 is somy of mother and n_(c)is somy of the child, (1 for monosomy, 2 for disomy, 3 for trisomy).cf_(correct) is corrected fraction of the child in the mixture

${cf}_{correct} = {{cf}*\frac{n_{c}}{{n_{m}*\left( {1 - {cf}} \right)} + {n_{c}*{cf}}}}$

If child is a disomy cf_(correct)=cf, but for a trisomy fraction of thechild in the mix for this chromosome is actually a bit higher

${cf}_{correct} = {{cf}*{\frac{3}{2 + {cf}}.}}$

In a more complex case where there is not exact alignment, X is acombination of binomials integrated over possible Di reads per SNP.

Using a Joint Distribution Model: LIK(H) for a Composite Hypothesis

In real life, trisomy is usually not purely matched or unmatched, due tocrossovers, so in this section results for composite hypotheses H21(maternal trisomy) and H12(paternal trisomy) are derived, which combinematched and unmatched trisomy, accounting for possible crossovers.

In the case of trisomy, if there were no crossovers, trisomy would besimply matched or unmatched trisomy. Matched trisomy is where childinherits two copies of the identical chromosome segment from one parent.Unmatched trisomy is where child inherits one copy of each homologouschromosome segment from the parent. Due to crossovers, some segments ofa chromosome may have matched trisomy, and other parts may haveunmatched trisomy. Described in this section is how to build a jointdistribution model for the heterozygosity rates for a set of alleles.

Suppose that on SNP i, LIK(i, Hm) is the fit for matched hypothesis H,and LIK(i, Hu) is the fit for UNmatched hypothesis H, andpc(i)=probability of crossover between SNPs i−1,i. One may thencalculate the full likelihood as:

LIK(H)=Σ_(S,E) LIK(S,E,1:N)

where LIK(S, E, 1: N) is the likelihood starting with hypothesis S,ending in hypothesis E, for SNPs 1:N. S=hypothesis of the first SNP,E=hypothesis of the last SNP, S,Eε(Hm, Hu). Recursively one maycalculate:

LIK(S,E,1:i)=LIK(i,E)+log(exp(LIK(S,E,1:i−1))*(1−pc(i))+exp(LIK(S,˜E,1:i−1))*pc(i))

where ˜E is the other hypothesis (not E). In particular, one maycalculate the likelihood of 1:i SNPs, based on likelihood of 1:(i−1)SNPs with either the same hypothesis and no crossover or the oppositehypothesis and a crossover times the likelihood of the SNP iFor SNP i=1: LIK(S, E, 1:1)={_(0 if S≠E) ^(LIK(1,S) if S=E) Thencalculate:

LIK(S,E,1:2)=LIK(2,E)+log(exp(LIK(S,E,1))*(1−pc(2))+exp(LIK(S,˜E,1))*pc(2))

And so on until i=N.

Deriving Child Fraction

The above formulas assume a known child fraction, which is not alwaysthe case. In one embodiment, it is possible to find the most likelychild fraction by maximizing the likelihood for disomy on selectedchromosomes.

In particular, supposes that LIK(chr, H11, cf)=log likelihood asdescribed above, for the disomy hypothesis, and for child fraction cf onchromosome chr. For selected chromosomes in Cset (usually 1:16). Thenthe full likelihood is:

LIK(cf)=Σ_(chrεCset) Lik(chr,H11,cf) and cf*=argmax_(cf) LIK(cf).

It is possible to use any set of chromosomes. It is also possible toderive child fraction without paternal data, as follows:Deriving Copy Number without Paternal Data

Recall the formula of the simple hypothesis log likelihood on SNP i

$\begin{matrix}{{L\; I\; {K\left( {i,H} \right)}} = {\log \; {{lik}\left( {{x_{i}m_{i}},f_{i},H,{cf}} \right)}}} \\{= {\sum\limits_{c}{{p\left( {{cm_{i}},f_{i},H} \right)}*\log \; {{lik}\left( {{x_{i}m_{i}},c,H,{cf}} \right)}}}}\end{matrix}$

Determining the probability of the true child given parents p(c|m_(i),f_(i), H) requires the knowledge of father genotype. If the fathergenotype is unknown, but pA_(i), the population frequency of A allele onthis SNP, is known, it is possible to approximate the above likelihoodwith

LIK(i,H)=log lik(x _(i) ,|m _(i) ,f _(i) ,H,cf)=Σ_(c) p(c|m _(i) ,H)*loglik(x _(i) ,|m _(i) ,c,H,cf) where

${p\left( {{cm_{i}},H} \right)} = {\sum\limits_{f}{{p\left( {{cm_{i}},f,H} \right)}*{p\left( {f{pA}_{i}} \right)}}}$

where p(f|pA_(i)) is the probability of particular father genotype,given the frequency of A on SNP i.In particular:

p(AA|pA _(i))=(pA _(i))² ,p(AB|pA _(i))=2(pA _(i))*(1−pA _(i)),p(BB|pA_(i))=(1−pA _(i))²

Incorporating Data Dropouts

Elsewhere in this disclosure it has been assumed that the probability ofgetting an A is a direct function of the true mother genotype, the truechild genotype, the fraction of the child in the mix, and the child copynumber. It is also possible that mother or child alleles can drop out,for example instead of having true child AB in the mix, there is only A,in which case the chance of getting a nexus sequence measurement of Aare much higher. Assume that mother dropout rate is MDO, and childdropout rate is CDO. In some embodiments, the mother dropout rate can beassumed to be zero, and child dropout rates are relatively low, so theresults in practice are not severely affected by dropouts. Nonetheless,they have been incorporated into the algorithm here. Elsewhere,lik(x_(i)|m_(i),c,cf)=pdf_(X)(x_(i)) has been defined as the likelihoodof getting x_(i) probability of A on SNP i, given sequence measurementsS, assuming true mother m_(i), true child c. If there is a dropout inthe mother or child, the input data is NOT true mother(m_(i)) orchild(c), but mother after possible dropout (m_(d)) and child after apossible dropout (c_(d)). One can then rewrite the above formula as

${{lik}\left( {{x_{i}m_{i}},c,{cf}} \right)} = {\sum\limits_{m_{d},c_{d}}{{p\left( {m_{d}m_{i}} \right)}*{p\left( {c_{d}c} \right)}*{{lik}\left( {{x_{i}m_{d}},c_{d},{cf}} \right)}}}$

where p(m_(d)|m_(i)) is the probability of new mother genotype m_(d),given true mother genotype m_(i), assuming dropout rate mdo, andp(c_(d)|c) is the probability of new child genotype c_(d), given truechild genotype c, assuming dropout rate CDO. If nA_(T)=number of Aalleles in true genotype c, nA_(D)=number of A alleles in ‘drop’genotype c_(d), where nA_(T)≧nA_(D), and similarly nB_(T)=number of Balleles in true genotype c, nB_(D)=number of B alleles in ‘drop’genotype c_(d), where nB_(T)≧nB_(D) and d=dropout rate, then

p(c _(d) |c)=(_(nA) _(D) ^(nA) ^(T) )*d ^(nAs) ^(T) ^(-nA) ^(D)*(1−d)^(nA) ^(D) *(_(nB) _(D) ^(nB) ^(T) )*d ^(nBs) ^(T) ^(-nB) ^(D)*(1−d)^(nB) ^(D)

For one set of experimental data, the parent genotypes have beenmeasured, as well as the true child genotype, where the child hasmaternal trisomy on chromosomes 14 and 21. Sequencing measurements havebeen simulated for varying values of child fraction, N distinct SNPs,and total number of reads NR. From this data it is possible to derivethe most likely child fraction, and derive copy number assuming known orderived child fraction.

The simulated and estimate child fraction are shown in FIG. 2 for N=700,NR=700,000. The hit rate versus child fraction is shown in FIGS. 3A-3Efor N=200 and varying NR, derived copy number hit rate, for true copynumber=H11 or H21, versus true child fraction.

The hit rate versus confidence is shown in FIGS. 4 and 5 for copy numberestimates with combined results for N=200, all child fractions and NR,given as confidence bars and hit rates. The hit rate versus confidenceis shown in FIGS. 6A and 6B for copy number estimates with combinedresults for N=200, all child fractions and NR, checking concordance ofhit rates and given confidences, for range of confidence>90%, with errorbars. An estimated versus true dropout rate is shown in FIGS. 7A and 7Bfor child fraction=0.05 and 0.1, N=700, NR=700,000; child dropout rateswere estimated for a range of true dropout rates. The mother dropoutrate is assumed to be zero. FIGS. 8A-8E show hit rates versus childfraction when the method includes a dropout model, assuming 5% dropoutrate.

In one embodiment, the method disclosed herein can be used to determinea fetal aneuploidy by determining the number of copies of maternal andfetal target chromosomes, having target sequences in a mixture ofmaternal and fetal genetic material. This method may entail obtainingmaternal tissue containing both maternal and fetal genetic material; insome embodiments this maternal tissue may be maternal plasma or a tissueisolated from maternal blood. This method may also entail obtaining amixture of maternal and fetal genetic material from said maternal tissueby processing the aforementioned maternal tissue. This method may entaildistributing the genetic material obtained into a plurality of reactionsamples, to randomly provide individual reaction samples that contain atarget sequence from a target chromosome and individual reaction samplesthat do not contain a target sequence from a target chromosome, forexample, performing high throughput sequencing on the sample. Thismethod may entail analyzing the target sequences of genetic materialpresent or absent in said individual reaction samples to provide a firstnumber of binary results representing presence or absence of apresumably euploid fetal chromosome in the reaction samples and a secondnumber of binary results representing presence or absence of a possiblyaneuploid fetal chromosome in the reaction samples. Either of the numberof binary results may be calculated, for example, by way of aninformatics technique that counts sequence reads that map to aparticular chromosome, to a particular region of a chromosome, to aparticular locus or set of loci. This method may involve normalizing thenumber of binary events based on the chromosome length, the length ofthe region of the chromosome, or the number of loci in the set. Thismethod may entail calculating an expected distribution of the number ofbinary results for a presumably euploid fetal chromosome in the reactionsamples using the first number. This method may entail calculating anexpected distribution of the number of binary results for a presumablyaneuploid fetal chromosome in the reaction samples using the firstnumber and an estimated fraction of fetal DNA found in the mixture, forexample, by multiplying the expected read count distribution of thenumber of binary results for a presumably euploid fetal chromosome by(1+n/2) where n is the estimated fetal fraction. The fetal fraction maybe estimated by a plurality of methods, some of which are describedelsewhere in this disclosure. This method may involve using a maximumlikelihood approach to determine whether the second number correspondsto the possibly aneuploid fetal chromosome being euploid or beinganeuploid. This method may involve calling the ploidy status of thefetus to be the ploidy state that corresponds to the hypothesis with themaximum likelihood of being correct given the measured data.

Using LIPs Plus Sequencing for Ploidy Calling

All data used in the following analysis is primary data as reported inthe following publication: Porreca et al., Nature Methods, 2007 4(11),p. 931-936. In an embodiment, the present disclosure relates to a methodfor determining ploidy state of an individual given the genotypic dataas output from a sequencing platform, where the genomic data has beenamplified using a massively multiplex amplification procedure involvingLIPs followed by ultra-high throughput sequencing.

The data set consists of 16 individuals. ˜13,000 MIPs probes wereselected. For each individual, 8 million reads were made, for atheoretical average read depth (number of reads/number of probes) of615.

The 8 million reads must be mapped to locations on a reference genome inorder to conduct analysis. This is done using the DNA Nexus web service.The processed data from DNA nexus contains the 8 million reads, in orderof genome position, along with their alignment and QC properties.

There are several possible ways to proceed. One may make the copy numbercall by the total number of reads, and not necessarily the number ofSNPs. Alternately, one may make the copy number call by the ratio ofreads containing each allele on heterozygous SNPs.

Read Count Analysis

Initially looking only at forward reads, consider the number of reads ateach position. If two reads have starting positions less than 5 basesapart, consider them the same and combine. This figure shows thedistribution of sequence count over the different positions. FIG. 9 isrepresentative of the data for each of the first 22 chromosomes; notethe log scale. The number of reads varies widely from one probe toanother. The plot for the last subject in FIG. 10 looks different. Notethat its percentile values look the same; 95th percentile depth of readis still about 1000.

FIGS. 11 and 12 show various percentiles of the sequence countdistributions as a function of the chromosome. The last chromosome shownis the X. The sample on the top is male, so the copy number for X ishalf that of the other chromosomes, which is clearly observable in thedata. The sample on the bottom is female.

These data indicate that the number of reads for a single sample varieswidely from one position to another. An important question in whetherthat variation is consistent across samples. If so, a model may becreated for each probe for how its number of reads varies from theaverage number of reads, given equal copy number. FIGS. 13A and 13Bconsider two samples (na10851 and na12156), one chromosome at a time.The plots show the correlation coefficient between the number of readsfor the two samples. The high correlation coefficient suggests thatvariation in the number of reads is due largely to probe characteristicsrather than variation between samples. (This data shows only forwardreads.)

Non-Invasive Prenatal Screening Using Allele Ratios

In one embodiment of the present disclosure, the disclosed method isused to detect fetal copy number by using genetic material found in amaternal blood sample, where the maternal blood sample contains somefree-floating fetal DNA. The fraction of fetal DNA compared to themother's DNA may be unknown. In one embodiment of the presentdisclosure, the ratio of the identity of alleles can be used todetermine the ploidy state of a fetus, as that ratio is characteristicof a given ploidy state. For example, if an individual is homogenous ata given allele, the ratio may be 1:0, if he is heterogeneous, it may be1:1; and if he is trisomic it could be 1:0 in the case of a homogenousallele, and 2:1 in the case of a heterogeneous allele. This ratio can behard to detect if it is in the presence of a large quantity of geneticmaterial from another individual whose ploidy state is different fromthe target individual. The method described herein is one way toaccomplish the ploidy determination of such an individual in such asituation. Some background for this method, including nomenclature,definitions, supporting mathematics, and other details may be found inU.S. Utility application Ser. No. 11/603,406, filed Nov. 28, 2006; U.S.Utility application Ser. No. 12/076,348, filed Mar. 17, 2008, and PCTUtility Application Serial No. PCT/US09/052730.

Claimed herein is a method to determine the ploidy state of a fetus fromthe fetal genetic material found in a maternal blood sample. The methodmay involve obtaining a maternal blood sample, and enriching the fetalDNA. The method may involve amplifying and/or genotyping or sequencingthe genetic material in the sample. It may involve using the methoddescribed herein to determine said ploidy state using data taken fromthe list comprising: the output of the genotyping, the sequence data,the determined allele identities, the allelic ratios, the intensities ofthe individual measurements, the separately measured haplotypic and/ordiploid genetic data from the mother, the haploid and diploid geneticdata from the father, genetic data from other related individuals, andcombinations thereof.

In one embodiment of the present disclosure, the results of the ploidydetermination may be used for the purpose of making a clinical decisionin the context of prenatal diagnosis, where said decision may involvedeciding to continue with the pregnancy, to terminate the pregnancy, toconduct further testing, and/or to make a medical intervention. Themethods described herein could be used in other contexts as well, forexample in archaeology, or forensics, where the goal is to determineploidy information or other genetic information, where the geneticmaterial from the target individual is in the presence of geneticmaterial from other individuals.

Some of the methods described herein are discussed in the context ofusing MIPs and/or sequencing, though any targeting and genotyping andtechnology could equally well apply. The alleles of interest may beSNPs, or they may be larger regions of DNA. The goal of the methodsdescribed herein is to determine genotypic data of the target individualin the presence of other, contaminating DNA, originating from otherindividuals. In one embodiment of the present disclosure, the genotypicdata that is desired involves the ploidy state of the target individual.In one embodiment of the present disclosure, the target DNA is fetalDNA, and thus the target individual is a gestating fetus, and where thefetal DNA is isolated, preferentially enriched, or simply measured inmaternal blood or plasma, and where the maternal DNA is the geneticmaterial from other individuals. The fetal DNA may be free floating,extracellular DNA, or it may be cellular DNA, for example, fromenucleated fetal red blood cells as found in maternal blood or plasmasamples. The genetic measurements of the DNA may be done using acombination of amplification methods, and genotyping methods, such asthose described in the patent applications listed in this document, andmay also include other methods such as rolling circle amplification,bridge sequencing, and other DNA amplification, genotyping andsequencing methods known in the art.

In some embodiments of the method, the parental genetic data may be usedto increase the accuracy with which the ploidy determination may bemade. In some embodiments of the method, the maternal genetic data maybe used to increase the accuracy with which the ploidy determination maybe made. In some embodiments, the knowledge of the maternal haplotypicgenetic data may be used along with the genetic data measured from freefloating DNA found in the blood to determine which haplotypes from themother and father are present in the fetus. This knowledge may be usedto determine the presence or absence of specific disease related genes,or other phenotypically correlated genes, in the genotype of the fetus.It may also be used to infer the more complete genotypic information ofthe fetus, specifically, allele calls, the presence of insertions,deletions, transpositions, and other genetic modifications that maycorrelate with diseases, conditions, or other phenotypes.

Simplified Explanation for Allele Ratio Method for Ploidy Calling in NPD

In one embodiment the ploidy state of a gestating fetus may bedetermined using a method that looks at allele ratios. Some methodsdetermine fetal ploidy state by comparing numerical sequencing outputDNA counts from a suspect chromosome to a reference euploid chromosome.In contrast to that concept, the allele ratio method determines fetalploidy state by looking at allele ratios for different parental contextson one chromosome. This method has no need to use a referencechromosome. For example, imagine the following possible ploidy states,and the allele ratios for various parental contexts:

(note: ratio ‘r’ is defined as follows: 1/r=fraction mother DNA/fractionfetal DNA)

A:B Child Parent A:B Child A:B Child P-M geno- context Euploidy genotypeP-U tri* genotype tri* type AA|BB 2 + r:r AB 2 + r: 2r ABB 2 + r:2r ABBBB|AA r:2 + r AB 2 + 2r:r AAB 2 + 2r:r AAB AA|AB 1:0 AA 2 + 2r:r AAB 1:0AAA AA|AB 2 + r:r AB — — 2 + 2r:r AAB AA|AB 4 + 2r:r average — — 4 +4r:r average *P-U tri = paternal matching trisomy; P-M tri = paternalmatching trisomy;

Note that this table represents only a subset of the parental contextsand a subset of the possible ploidy states that this method is designedto differentiate. In this case, one can determine the A:B ratios for aplurality of alleles from a set of parental contexts in a set ofsequencing data. One can then state a number of hypothesis for eachploidy state, and for each value of r; each hypothesis will have anexpected pattern of A:B ratios for the different parental contexts. Onecan then determine which hypothesis best fits the experimental data.

For example, using the above set of parental contexts, and the value ofr=0.2, one can rewrite the chart as follows: (For example, one cancalculate [# reads of allele A/# reads of allele B]; thus 2+r:r becomes2+0.2:0.2→2.2:0.2=11)

A/B A/B Parent A/B Child P-U Child P-M Child context Euploidy genotypetri* genotype tri* genotype AA|BB 11 AB 5.5 ABB 5.5 ABB BB|AA 0.91 AB 12AAB 12 AAB AA|AB infinte AA 12 AAB infinite AAA AA|AB 11 AB — — 12 AABAA|AB 21 average — — 44 average

Now, one can look at the ratios between the A:B ratios for differentparental contexts. In this case, one may expect theA:B_(AA|BB)/A:B_(AA|AB) to be 11/21=0.524 on average for euploidy; to be5.5/12=0.458 on average for a paternal unmatched trisomy, and5.5/44=0.125 on average for a paternal matching trisomy. The profile ofA:B ratios among different contexts will be different for differentploidy states, and the profiles should be distinctive enough that itwill be possible to determine the ploidy state for a chromosome withhigh accuracy. Note that the calculated value of r may be determinedusing a different method, or it can be determined using a maximumlikelihood approach to this method. In one embodiment, the methodrequires the maternal genotypic knowledge. In one embodiment the methodrequires paternal genotypic knowledge. In one embodiment the method doesnot require paternal genotypic knowledge. In an embodiment, the percentfetal fraction and the ratio of maternal to fetal DNA are essentiallyequivalent, and can be used interchangeably after applying theappropriate linear algebraic transformation. In some embodiments,r=[percent fetal fraction]/[1−percent fetal fraction].

Allele Ratio Analysis at SNPs

The SNP130 database has been linked with Matlab in order to identifysequences that have SNPs in them. The goal is to determine how well theobserved allele ratio reflects expected allele ratio in genotype. Theseare healthy adult samples, so SNPs should either be homozygous, in whichcase they should have a 1:0 allele ration, or heterozygous, in whichcase they should have a 1:1 allele ratio.

FIGS. 14 and 15 show the allele ratios at all SNPs as a function of thenumber of sequences. All mapped sequences are included for which thereis a base call at the SNP location (i.e., no minimum phred score isrequired). The dotted lines show 1-sigma bounds for the observed rate,modeling each sequence as an independent Bernoulli trial. Note that thex-axis varies between plots.

SNP Classification Using Phred Scores

The phred score, q, is defined as follows: P(wrong base call)=10̂(−q/10)Let x=reference ratio of true genotype=number of referencealleles/number of total alleles. For disomy, x in {0, 0.5, 1}corresponds to {MM, RM, RR}. Let z be the allele observed in a sequence,z in {R, M}. Here the likelihood of observing z=R is shown, conditionedon the true ratio of reference alleles in the genotype (ie, what isP(z=R|x)

P(z=R|x)=P(z=R|gc,x)P(gc)+P(z=R|bc,x)P(bc)

where gc is the event of a correct call and be is the event of a badcall.

P(gc) and P(bc) are calculated from the phred score. P(z=R|gc,x)=x andP(z=R|bc,x)=1−x, assuming that probes are unbiased.

Result, where b=P(wrong base call): P(z=R|x)=x(1−b)+(1−x)*b

Note that the probability of a reference allele measurement converges tothe reference allele ratio as the phred score improves, as expected.

Assuming that each sequence is generated independently, conditioned onthe true genotype, the likelihood of a set of measurements at the sameSNP is simply the product of the individual likelihoods. This methodaccounts for varying phred scores. In another embodiment, it is possibleto account for varying confidence in the sequence mapping. Given the setof n sequences for a single SNP, the combination of likelihoods resultsin a polynomial of order n that can be evaluated at the candidate alleleratios that represent the various hypotheses.

SNP Classification Using Phred Threshold

When a large number of sequences are available for a single SNP, thepolynomial likelihood function on the allele ratio becomes intractable.An alternative is to consider only the base calls which have high phredscore, and then assume that they are accurate. Each base read is now anIID Bernoulli according to the true allele ratio, and the likelihoodfunction is Gaussian. If r is the ratio of reference reads in the data,the likelihood function on x (the true reference allele ratio) hasmean=r and standard deviation=sqrt(r*(1−r)/n).

SNP Bias Correlation across Samples

Using the two likelihood functions discussed above (polynomial,Gaussian) a SNP can be classified as RR, RM, or MM by considering theallele ratios {1, 0.5, 0}, or a maximum likelihood estimate of theallele ratio can be calculated. When the same SNP is classified as RM intwo different samples, it is possible to compare the MLE estimates ofthe allele ratio to look for consistent “probe bias.”

From four samples, SNPs were taken where exactly two samples areclassified as RM, and plotted are the MLE allele ratios for thosesamples. If all probes were perfectly unbiased, the dots should beclustered at (0.5, 0.5). If the probes had perfectly consistent bias,the dots would lie along the 1:1 line, subject to some standarddeviation. FIG. 16 shows 159 SNPs that were classified RM on twosamples. Note that some dots lie on the perimeter of the plot, showingthat the MLE estimate of the allele ratio disagrees with theclassification.

Accuracy of Phred Scores

The goal here is to verify that phred scores reflect accuracy of basecalls according to their definition. P(correct)=1−10̂(−q/10) where q isthe phred score.

For simplicity, select sequences that do not contain a SNP. Use thereference sequence as truth. Phred scores range from 0 to 30 and arereported as integers; in this case integer bins are used. Count thenumber of bases in each bin, and the number of reference calls in eachbin. FIG. 17A (top) shows data from chromosome 1 of one sample, a totalof 63 million base calls. Bases which are “no-call” are reported withphred score=0, and therefore not included. FIG. 17B (bottom) uses analternative definition for the phred score which was used in olderversions of this sequencing platform. This prediction more closelymatches the data.

These plots suggest that low phred scores may not be the best predictorsof whether or not a base call is accurate. However, a high phred scoreis reflective of high accuracy in the base call, and there are many suchcalls. Therefore, one may set a threshold on phred score rather thantrying to incorporate it into likelihood calculations.

Using Sequence Length as a Prior to Determine the Origin of DNA

It has been reported that the distribution of length of sequences differfor maternal and fetal DNA, with fetal generally being shorter. In oneembodiment of the present disclosure, it is possible to use previousknowledge in the form of empirical data, and construct priordistribution for expected length of both mother(P(X|maternal)) and fetalDNA (P(X|fetal)). Given new unidentified DNA sequence of length x, it ispossible to assign a probability that a given sequence of DNA is eithermaternal or fetal DNA, based on prior likelihood of x given eithermaternal or fetal. In particular if P(x|maternal)>P(x|fetal), then theDNA sequence can be classified as maternal, withP(x|maternal)=P(x|maternal)/[(P(x|maternal)+P(x|fetal)], and ifp(x|maternal)<p(x|fetal), then the DNA sequence can be classified asfetal, P(x|fetal)=P(x|fetal)/[(P(x|maternal)+P(x|fetal)]. In oneembodiment of the present disclosure, a distributions of maternal andfetal sequence lengths can be determined that is specific for thatsample by considering the sequences that can be assigned as maternal orfetal with high probability, and then that sample specific distributioncan be used as the expected size distribution for that sample.

Variable Read Depth to Minimize Sequencing Cost

In many clinical trials concerning a diagnostic, for example, in Chiu etal. BMJ 2011; 342:c7401, a protocol with a number of parameters is set,and then the same protocol is executed with the same parameters for eachof the patients in the trial. In the case of determining the ploidystatus of a fetus gestating in a mother using sequencing as a method tomeasure genetic material one pertinent parameter is the number of reads.The number of reads may refer to the number of actual reads, the numberof intended reads, fractional lanes, full lanes, or full flow cells on asequencer. In these studies, the number of reads is typically set at alevel that will ensure that all or nearly all of the samples achieve thedesired level of accuracy. Sequencing is currently an expensivetechnology, a cost of roughly $200 per 5 mappable million reads, andwhile the price is dropping, any method which allows a sequencing baseddiagnostic to operate at a similar level of accuracy but with fewerreads will necessarily save a considerable amount of money.

The accuracy of a ploidy determination is typically dependent on anumber of factors, including the number of reads and the fraction offetal DNA in the mixture. The accuracy is typically higher when thefraction of fetal DNA in the mixture is higher. At the same time, theaccuracy is typically higher if the number of reads is greater. It ispossible to have a situation with two cases where the ploidy state isdetermined with comparable accuracies wherein the first case has a lowerfraction of fetal DNA in the mixture than the second, and more readswere sequenced in the first case than the second. It is possible to usethe estimated fraction of fetal DNA in the mixture as a guide indetermining the number of reads necessary to achieve a given level ofaccuracy.

In an embodiment of the present disclosure, a set of samples can be runwhere different samples in the set are sequenced to different readsdepths, wherein the number of reads run on each of the samples is chosento achieve a given level of accuracy given the calculated fraction offetal DNA in each mixture. In one embodiment of the present disclosure,this may entail making a measurement of the mixed sample to determinethe fraction of fetal DNA in the mixture; this estimation of the fetalfraction may be done with sequencing, it may be done with TaqMan, it maybe done with qPCR, it may be done with SNP arrays, it may be done withany method that can distinguish different alleles at a given loci. Theneed for a fetal fraction estimate may be eliminated by includinghypotheses that cover all or a selected set of fetal fractions in theset of hypotheses that are considered when comparing to the actualmeasured data. After the fraction fetal DNA in the mixture has beendetermined, the number of sequences to be read for each sample may bedetermined.

In one embodiment of the present disclosure, 100 pregnant women visittheir respective OB's, and their blood is drawn into blood tubes with ananti-lysant. They each take home a kit for the father of their gestatingfetus who gives a saliva sample. Both sets of genetic materials for all100 couples are sent back to the laboratory, where the mother blood isspun down and the buffy coat is isolated, as well as the serum. Theserum contains a mixture of maternal DNA as well as placentally derivedDNA. The maternal buffy coat and the paternal blood is genotyped using aSNP array, and the DNA in the maternal plasma samples are targeted withSURESELECT hybridization probes. The DNA that was pulled down with theprobes is used to generate 100 tagged libraries, one for each of thematernal samples, where each sample is tagged with a different tag. Afraction from each library is withdrawn, each of those fractions aremixed together and added to two lanes of a ILLUMINA HISEQ DNA sequencerin a multiplexed fashion, wherein each lane resulted in approximately 50million mappable reads, resulting in approximately 100 million mappablereads on the 100 multiplexed mixtures, or approximately 1 million readsper sample. The sequence reads were used to determine the fraction offetal DNA in each mixture. 50 of the samples had more than 15% fetal DNAin the mixture, and the 1 million reads were sufficient to determine theploidy status of the fetuses with a 99.9% confidence.

Of the remaining mixtures, 25 had between 10 and 15% fetal DNA; afraction of each of the relevant libraries prepped from these mixtureswere multiplexed and run down one lane of the HISEQ generating anadditional 2 million reads for each sample. The two sets of sequencedata for each of the mixture with between 10 and 15% fetal DNA wereadded together, and the resulting 3 million reads per sample which weresufficient to determine the ploidy state of those fetuses with 99.9%confidence.

Of the remaining mixtures, 13 had between 6 and 10% fetal DNA; afraction of each of the relevant libraries prepped from these mixtureswere multiplexed and run down one lane of the HISEQ generating anadditional 4 million reads for each sample. The two sets of sequencedata for each of the mixture with between 6 and 10% fetal DNA were addedtogether, and the resulting 5 million total reads per mixture which weresufficient to determine the ploidy state of those fetuses with 99.9%confidence.

Of the remaining mixtures, 8 had between 4 and 6% fetal DNA; a fractionof each of the relevant libraries prepped from these mixtures weremultiplexed and run down one lane of the HISEQ generating an additional6 million reads for each sample. The two sets of sequence data for eachof the mixture with between 4 and 6% fetal DNA were added together, andthe resulting 7 million total reads per mixture which were sufficient todetermine the ploidy state of those fetuses with 99.9% confidence.

Of the remaining four mixtures, all of them had between 2 and 4% fetalDNA; a fraction of each of the relevant libraries prepped from thesemixtures were multiplexed and run down one lane of the HISEQ generatingan additional 12 million reads for each sample. The two sets of sequencedata for each of the mixture with between 2 and 4% fetal DNA were addedtogether, and the resulting 13 million total reads per mixture whichwere sufficient to determine the ploidy state of those fetuses with99.9% confidence.

This method required six lanes of sequencing on a HISEQ machine toachieve 99.9% accuracy over 100 samples. If the same number of runs hadbeen required for every sample, to ensure that every ploidydetermination was made with a 99.9% accuracy, it would have taken 25lanes of sequencing, and if a no-call rate or error rate of 4% wastolerated, it could have been achieved with 14 lanes of sequencing.

According to some embodiments, the congenital disorder is amalformation, neural tube defect, chromosome abnormality, Down syndrome(or trisomy 21), Trisomy 18, spina bifida, cleft palate, Tay Sachsdisease, sickle cell anemia, thalassemia, cystic fibrosis, Huntington'sdisease, and/or fragile x syndrome. Chromosome abnormalities include,but are not limited to, Down syndrome (extra chromosome 21), TurnerSyndrome (45X0) and Klinefelter's syndrome (a male with 2 Xchromosomes).

According to some embodiments, the malformation is a limb malformation.Limb malformations include, but are not limited to, amelia,ectrodactyly, phocomelia, polymelia, polydactyly, syndactyly,polysyndactyly, oligodactyly, brachydactyly, achondroplasia, congenitalaplasia or hypoplasia, amniotic band syndrome, and cleidocranialdysostosis.

According to some embodiments, the malformation is a congenitalmalformation of the heart. Congenital malformations of the heartinclude, but are not limited to, patent ductus arteriosus, atrial septaldefect, ventricular septal defect, and tetralogy of fallot.

According to some embodiments, the malformation is a congenitalmalformation of the nervous system. Congenital malformations of thenervous system include, but are not limited to, neural tube defects(e.g., spina bifida, meningocele, meningomyelocele, encephalocele andanencephaly), Arnold-Chiari malformation, the Dandy-Walker malformation,hydrocephalus, microencephaly, megencephaly, lissencephaly,polymicrogyria, holoprosencephaly, and agenesis of the corpus callosum.

According to some embodiments, the malformation is a congenitalmalformation of the gastrointestinal system. Congenital malformations ofthe gastrointestinal system include, but are not limited to, stenosis,atresia, and imperforate anus.

According to some embodiments, the systems, methods, and techniques ofthe present disclosure are used in methods to increase the probabilityof implanting an embryo obtained by in vitro fertilization that is at areduced risk of carrying a predisposition for a genetic disease.

According to some embodiments, the genetic disease is either monogenicor multigenic. Genetic diseases include, but are not limited to, BloomSyndrome, Canavan Disease, Cystic fibrosis, Familial Dysautonomia,Riley-Day syndrome, Fanconi Anemia (Group C), Gaucher Disease, Glycogenstorage disease 1a, Maple syrup urine disease, Mucolipidosis IV,Niemann-Pick Disease, Tay-Sachs disease, Beta thalessemia, Sickle cellanemia, Alpha thalessemia, Beta thalessemia, Factor XI Deficiency,Friedreich's Ataxia, MCAD, Parkinson disease—juvenile, Connexin26, SMA,Rett syndrome, Phenylketonuria, Becker Muscular Dystrophy, DuchennesMuscular Dystrophy, Fragile X syndrome, Hemophilia A, Alzheimerdementia—early onset, Breast/Ovarian cancer, Colon cancer,Diabetes/MODY, Huntington disease, Myotonic Muscular Dystrophy,Parkinson Disease—early onset, Peutz-Jeghers syndrome, Polycystic KidneyDisease, Torsion Dystonia.

In some embodiments, the method may further comprise administeringprenatal or post-natal treatments for the congenital disorder. In someembodiments, the method may further comprise determining whether thefetus is likely to be afflicted with a malformation. In someembodiments, the method may further comprise administering prenatal orpost-natal treatments for the malformation. In some embodiments, themethod may further comprise determining whether the fetus is likely tobe afflicted with a genetic disease. In some embodiments, the method mayfurther comprise administering prenatal or post-natal treatments for thegenetic disease. In some embodiments, the prenatal or post-nataltreatment is taken from the group comprising pharmaceutical basedintervention, surgery, genetic therapy, nutritional therapy, orcombinations thereof. In some embodiments, the method may furthercomprise generating a report containing information pertaining to thedetermination. In some embodiments, the report may contain informationpertaining to the determination as determined in any preceding orsubsequent claim. In some embodiments, the method may further comprisegenerating a report containing the likelihood of a fetus displaying aphenotype, wherein the likelihood of the fetus displaying the phenotypewas estimated using the determination as determined in any preceding orsubsequent claim. In some embodiments, the method may further compriseperforming a pregnancy termination.

Note that it has been demonstrated that DNA that originated from cancerthat is living in a host can be found in the blood of the host. In thesame way that genetic diagnoses can be made from the measurement ofmixed DNA found in maternal blood, genetic diagnoses can equally well bemade from the measurement of mixed DNA found in host blood. The geneticdiagnoses may include aneuploidy states, or gene mutations. Any claim inthat patent that reads on determining the ploidy state or genetic stateof a fetus from the measurements made on maternal blood can equally wellread on determining the ploidy state or genetic state of a cancer fromthe measurements on host blood.

In some embodiments, the method may allow one to determine the ploidystatus of a cancer, the method comprising obtaining a mixed sample thatcontains genetic material from the host, and genetic material from thecancer, measuring the DNA in the mixed sample, calculating the fractionof DNA that is of cancer origin in the mixed sample, and determining theploidy status of the cancer using the measurements made on the mixedsample and the calculated fraction. In some embodiments, the method mayfurther comprise administering a cancer therapeutic based on thedetermination of the ploidy state of the cancer. In some embodiments,the method may further comprise administering a cancer therapeutic basedon the determination of the ploidy state of the cancer, wherein thecancer therapeutic is taken from the group comprising a pharmaceutical,a biologic therapeutic, and antibody based therapy and combinationthereof

Context Optimization

A method which can provide more information for a given number of reads,or alternately, require a fewer number of reads for a given level ofaccuracy, is to focus on reads that cover SNPs, where the context of theparents are known at that SNP. Furthermore, there are a number ofmethods, such as circularizing probes or capture probes, for targetingspecific SNPs that can enhance the number of reads that map to thoseSNPs. In a targeted approach to sequencing maternal plasma the questionthen becomes, which SNPs should one target? In general, the mostinformative context is AA|BB, because for every such SNP, the child willbe AB, and the measurements of the B allele will not be contaminated bymaternal DNA. The second most informative context is AA|AB, because halfof the fetal alleles in that context will be AB. In the AA|BB context,there is a 100% chance that there is a fetal allele that is a HISNP. Inthe AA|AB context, there is a 50% chance that there is a fetal allelethat is a HISNP. The remaining three contexts are of different levels ofinformativeness for given situations. Note, for reasons of symmetry, thenine contexts can be collapsed into five; e.g. AB|AA is effectively thesame as AB|AA)

In one embodiment of the present disclosure, a method is presented forselecting SNPs for targeting that maximizes the chance of obtainingmaximally informative SNPs. In one embodiment of the present disclosure,the set of SNPs with the highest minor allele frequency are selected fortargeting. The maximum minor allele frequency possible is 50%. From aset of SNPs with known minor allele frequencies, those with the highestminor allele frequency may be selected. In some embodiments of thepresent disclosure, the SNPs are selected where the parent contextsmaximize the chance that the fetus will have a HISNP at that locus. Notethat when no apriori knowledge of the actual parental contexts isavailable, those loci with the highest minor allele frequency willresult in the maximal likelihood of the fetus having a HISNP at thatallele. In cases where the mother's genotype is known, one may choosethose alleles that are homozygous, since only when a maternal context ishomozygous is it possible for the fetus to have a HISNP. If the father'sgenotype is known, those loci may be chosen where the father's contextis homozygous for allele that is the minor allele in the population.Alternately, those loci may be chosen where the paternal context isheterozygous. In the case where the parental genotypes are both known,those loci may be chosen that are from the AA|BB context. Alternately,those loci may be chosen that are from the AA|AB context.

In some cases, three alleles may have some frequency in the population,(e.g. A, T and G). In some embodiments of the present disclosure, theset of SNPs where the sum of the minor allele frequencies are greatestare selected for targeting. In some embodiments of the presentdisclosure, the set of SNPs for targeting is selected by selecting locithat maximize the chance that the fetus will have a HISNP at that locus.Note that a locus where the allele frequencies that are 60%/40% will notbe as likely to result in a fetal allele that is a HISNP as a contextthat is, for example, 60%/30%/10%.

In some cases, different populations may have different allelefrequencies. In cases where there is no a priori knowledge of theparental genotypes, but the parents are from different population groupswhere those two populations have different allele frequencies at someloci, then it is possible to choose loci to target that provide agreater likelihood of the fetus having a HISNP that by using one overallpopulation allele frequency model.

In a case where the two parents are of a different ethnicity, one way tomaximize the likelihood of a given SNP being from a highly informativeparental context is to choose a set of SNPs where the heterozygosity isas low as possible but different from one another. For example, if themother is Caucasian and the father is Asian, and within the Caucasianpopulation the SNP has a frequency of 40% T and 60% G, and within theAsian population the SNP has a frequency of 60% T and 40% G, then thefrequency of the parental context is AA|BB at that SNP is greater than⅛.

Imagine a couple from two different population groups, and two sets ofloci where the minor allele frequency is as follows for the twopopulation groups: locus set #1: 0.5 and 0.3, locus set #2: 0.4 and 0.4?The (0.5/0.3) locus set will contain, on average, 14.5% of SNPs with theAA|BB parental context, while the (0.4/0.4) locus set will contain, onaverage, 11.52% of SNPs with the AA|BB parental context. At the sametime, the (0.5/0.3) locus set will contain, on average, 21.0% of SNPswith the AA|AB parental context, while the (0.4/0.4) locus set willcontain, on average, 25.0% of SNPs with the AA|AB parental context.Since the AA|BB context always results in a HISNP, and the AA|AB contextresults in a HISNP half of the time, the (0.5/0.3) locus set willcontain, on average, 25.0% fetal HISNP, and the (0.4/0.4) locus set willcontain, on average, 24.0% fetal HISNPs. In one embodiment of thepresent disclosure, one may select SNPs for targeting in whichheterozygosity rate (a term which is used here interchangeably with theterm minor allele frequency) among the father's population is maximized,but the minor allele frequency among the mother's population group isminimized.

Using Raw Genotyping Data

There are a number of methods that can accomplish NPD using fetalgenetic information measured on fetal DNA found in maternal blood. Someof these methods involve making measurements of the fetal DNA using SNParrays, some methods involve untargeted sequencing, and some methodsinvolve targeted sequencing. The targeted sequencing may target SNPs, itmay target STRs, it may target other loci, or is may target somecombination of those loci. In some of these methods, the method mayinvolve using a commercial or proprietary allele caller than calls theidentity of the alleles from the intensity data that comes from thesensors in the machine doing the measuring. For example, the ILLUMINAINFINIUM system or the AFFYMETRIX GENECHIP microarray system involvesbeads or microchips with attached DNA sequences that can hybridize tocomplementary segments of DNA. There are also sequencing methods, forexample the ILLUMINA SOLEXA GENOME SEQUENCER or the ABI SOLID GENOMESEQUENCER, wherein the genetic sequence of fragments of DNA aresequenced. In all of these methods the genotypic or sequencing data istypically determined on the basis of fluorescent signals (or the lackthereof). These systems typically are combined with low level softwarepackages that make specific allele calls (secondary genetic data) fromthe analog output of the fluorescent or other detection device (primarygenetic data). For example, in the case of a given allele on a SNParray, the software will make a call, for example, that a certain SNP ispresent or not present if the fluorescent intensity is measure above orbelow a certain threshold. Similarly, the output of a sequencer is achromatogram that indicates the level of fluorescence detected for eachof the dyes, and the software will make a call that a certain base pairis A or T or C or G. High throughput sequencers typically make a seriesof such measurements, called a read, that represents the most likelystructure of the DNA sequence that was sequenced. The direct analogoutput of the chromatogram is defined here to be the primary geneticdata, and the base pair/SNP calls made by the software are consideredhere to be the secondary genetic data. In one embodiment, primary datarefers to the raw intensity data that is the unprocessed output of agenotyping platform, where the genotyping platform may refer to a SNParray, or to a sequencing platform. The secondary genetic data refers tothe processed genetic data, where an allele call has been made, or thesequence data has been assigned base pairs, and/or the sequence readshave been mapped to the genome.

Many higher level applications take advantage of these allele calls, SNPcalls and sequence reads, that is, the secondary genetic data, that thegenotyping software produces. For example, DNA NEXUS, ELAND or MAQ willtake the sequencing reads and map them to the genome. For example, inthe context of non-invasive prenatal diagnosis, complex informatics,such as PARENTAL SUPPORT™, may leverage a large number of SNP calls todetermine the genotype of an individual. Also, in the context ofpreimplantation genetic diagnosis, it is possible to take a set ofsequence reads that are mapped to the genome, and by taking a normalizedcount of the reads that are mapped to each chromosome, or section of achromosome, it may be possible to determine the ploidy state of anindividual. In the context of non-invasive prenatal diagnosis it may bepossible to take a set of sequence reads that have been measured on DNApresent in maternal serum, and map them to the genome. One may then takea normalized count of the reads that are mapped to each chromosome, orsection of a chromosome, and use that data to determine the ploidy stateof an individual. For example, it may be possible to conclude that thosechromosomes that have a disproportionately large number of reads aretrisomic in the fetus that is gestating in the mother from which theblood was drawn.

However, in reality, the output of the measuring instruments is ananalog signal. When a certain base pair is called by the software thatis associated with the sequencing software, for example the software maycall the base pair a T, in reality the call is the call that thesoftware believes to be most likely. In some cases, however, the callmay be of low confidence, for example, the analog signal may indicatethat the particular base pair is only 90% likely to be a T, and 10%likely to be an A. In another example, the genotype calling softwarethat is associated with a SNP array reader may call a certain allele tobe GG. However, in reality, the underlying analog signal may indicatethat it is only 90% likely that the allele is GG, and 10% likely thatthe allele is GT. In these cases, when the higher level applications usethe genotype calls and sequence calls made by the lower level software,they are losing some information. That is, the primary genetic data, asmeasured directly by the genotyping platform, may be messier than thesecondary genetic data that is determined by the attached softwarepackages, but it contains more information. In mapping the secondarygenetic data sequences to the genome, many reads are thrown out becausesome bases are not read with enough clarity and or mapping is not clear.When the primary genetic data sequence reads are used, all or many ofthose reads that may have been thrown out when first converted tosecondary genetic data sequence read can be used by treating the readsin a probabilistic manner.

In one embodiment of the present disclosure, the higher level softwaredoes not rely on the allele calls, SNP calls, or sequence reads that aredetermined by the lower level software. Instead, the higher levelsoftware bases its calculations on the analog signals directly measuredfrom the genotyping platform. In one embodiment of the presentdisclosure, an informatics based method such as PARENTAL SUPPORT™ ismodified so that its ability to reconstruct the genetic data of theembryo/fetus/child is engineered to directly use the primary geneticdata as measured by the genotyping platform. In one embodiment of thepresent disclosure, an informatics based method such as PARENTALSUPPORT™ is able to make allele calls, and/or chromosome copy numbercalls using primary genetic data, and not using the secondary geneticdata. In one embodiment of the present disclosure, all genetic calls,SNPs calls, sequence reads, sequence mapping is treated in aprobabilistic manner by using the raw intensity data as measureddirectly by the genotyping platform, rather than converting the primarygenetic data to secondary genetic calls.

In some embodiments, the method can increase the accuracy of geneticdata of a target individual which incorporates genetic data of at leastone related individual, the method comprising obtaining primary geneticdata specific to a target individual's genome and genetic data specificto the genome(s) of the related individual(s), creating a set of one ormore hypotheses concerning which segments of which chromosomes from therelated individual(s) correspond to those segments in the targetindividual's genome, determining the probability of each of thehypotheses given the target individual's primary genetic data and therelated individual(s)'s genetic data, and using the probabilitiesassociated with each hypothesis to determine the most likely state ofthe actual genetic material of the target individual. In someembodiments, the method can determining the number of copies of asegment of a chromosome in the genome of a target individual, the methodcomprising creating a set of copy number hypotheses about how manycopies of the chromosome segment are present in the genome of a targetindividual, incorporating primary genetic data from the targetindividual and genetic information from one or more related individualsinto a data set, estimating the characteristics of the platform responseassociated with the data set, where the platform response may vary fromone experiment to another, computing the conditional probabilities ofeach copy number hypothesis, given the data set and the platformresponse characteristics, and determining the copy number of thechromosome segment based on the most probable copy number hypothesis. Inone embodiment, the method can determine a ploidy state of at least onechromosome in a target individual, the method comprising obtainingprimary genetic data from the target individual and from one or morerelated individuals, creating a set of at least one ploidy statehypothesis for each of the chromosomes of the target individual, usingone or more expert techniques to determine a statistical probability foreach ploidy state hypothesis in the set, for each expert technique used,given the obtained genetic data, combining, for each ploidy statehypothesis, the statistical probabilities as determined by the one ormore expert techniques, and determining the ploidy state for each of thechromosomes in the target individual based on the combined statisticalprobabilities of each of the ploidy state hypotheses. In one embodiment,the method can determine an allelic state in a set of alleles, in atarget individual, and from one or both parents of the targetindividual, and optionally from one or more related individuals, themethod comprising obtaining primary genetic data from the targetindividual, and from the one or both parents, and from any relatedindividuals, creating a set of at least one allelic hypothesis for thetarget individual, and for the one or both parents, and optionally forthe one or more related individuals, where the hypotheses describepossible allelic states in the set of alleles, determining a statisticalprobability for each allelic hypothesis in the set of hypotheses giventhe obtained genetic data, and determining the allelic state for each ofthe alleles in the set of alleles for the target individual, and for theone or both parents, and optionally for the one or more relatedindividuals, based on the statistical probabilities of each of theallelic hypotheses.

In some embodiments, the genetic data of the mixed sample may comprisesequence data wherein the sequence data may not uniquely map to thehuman genome. In some embodiments, the genetic data of the mixed samplemay comprise sequence data wherein the sequence data maps to a pluralityof locations in the genome, wherein each possible mapping is associatedwith a probability that the given mapping is correct. In someembodiments, the sequence reads are not assumed to be associated with aparticular position in the genome. In some embodiments, the sequencereads are associated with a plurality of positions in the genome, and anassociated probability belonging to that position.

Combining Methods of Prenatal Diagnosis

There are many methods that may be used for prenatal diagnosis orprenatal screening of aneuploidy or other genetic defects. Describedelsewhere in this document, and in U.S. Utility application Ser. No.11/603,406, filed Nov. 28, 2006; U.S. Utility application Ser. No.12/076,348, filed Mar. 17, 2008, and PCT Utility Application Serial No.PCT/S09/52730 is one such method that uses the genetic data of relatedindividuals to increase the accuracy with which genetic data of a targetindividual, such as a fetus, is known, or estimated. Other methods usedfor prenatal diagnosis involve measuring the levels of certain hormonesin maternal blood, where those hormones are correlated with variousgenetic abnormalities. An example of this is called the triple test, atest wherein the levels of several (commonly two, three, four or five)different hormones are measured in maternal blood. In a case wheremultiple methods are used to determine the likelihood of a givenoutcome, where none of the methods are definitive in and of themselves,it is possible to combine the information given by those methods to makea prediction that is more accurate than any of the individual methods.In the triple test, combining the information given by the threedifferent hormones can result in a prediction of genetic abnormalitiesthat is more accurate than the individual hormone levels may predict.

Disclosed herein is a method for making more accurate predictions aboutthe genetic state of a fetus, specifically the possibility of geneticabnormalities in a fetus, that comprises combining predictions ofgenetic abnormalities in a fetus where those predictions were made usinga variety of methods. A “more accurate” method may refer to a method fordiagnosing an abnormality that has a lower false negative rate at agiven false positive rate. In a favored embodiment of the presentdisclosure, one or more of the predictions are made based on the geneticdata known about the fetus, where the genetic knowledge was determinedusing the PARENTAL SUPPORT™ method, that is, using genetic data ofindividual related to the fetus to determine the genetic data of thefetus with greater accuracy. In some embodiments the genetic data mayinclude ploidy states of the fetus. In some embodiments, the geneticdata may refer to a set of allele calls on the genome of the fetus. Insome embodiments some of the predictions may have been made using thetriple test. In some embodiments, some of the predictions may have beenmade using measurements of other hormone levels in maternal blood. Insome embodiments, predictions made by methods considered diagnoses maybe combined with predictions made by methods considered screening. Insome embodiments, the method involves measuring maternal blood levels ofalpha-fetoprotein (AFP). In some embodiments, the method involvesmeasuring maternal blood levels of unconjugated estriol (UE₃). In someembodiments, the method involves measuring maternal blood levels of betahuman chorionic gonadotropin (beta-hCG). In some embodiments, the methodinvolves measuring maternal blood levels of invasive trophoblast antigen(ITA). In some embodiments, the method involves measuring maternal bloodlevels of inhibin. In some embodiments, the method involves measuringmaternal blood levels of pregnancy-associated plasma protein A (PAPP-A).In some embodiments, the method involves measuring maternal blood levelsof other hormones or maternal serum markers. In some embodiments, someof the predictions may have been made using other methods. In someembodiments, some of the predictions may have been made using a fullyintegrated test such as one that combines ultrasound and blood test ataround 12 weeks of pregnancy and a second blood test at around 16 weeks.In some embodiments, the method involves measuring the fetal nuchaltranslucency (NT). In some embodiments, the method involves using themeasured levels of the aforementioned hormones for making predictions.In some embodiments the method involves a combination of theaforementioned methods.

Combining the Predictions

There are many ways to combine the predictions, for example, one couldconvert the hormone measurements into a multiple of the median (MoM) andthen into likelihood ratios (LR). Similarly, other measurements could betransformed into LRs using the mixture model of NT distributions. TheLRs for NT and the biochemical markers could be multiplied by the ageand gestation-related risk to derive the risk for various conditions,such as trisomy 21. Detection rates (DRs) and false-positive rates(FPRs) could be calculated by taking the proportions with risks above agiven risk threshold.

Another method could involve a situation with four measured hormonelevels, where the probability distribution around those hormones isknown: p(x₁, x₂, x₃, x₄|e) for the euploid case and p(x₁, x₂, x₃, x₄|a)for the aneuploid case. Then one could measure the probabilitydistribution for the DNA measurements, g(y|e) and g(y|a) for the euploidand aneuploid cases respectively. Assuming they are independent giventhe assumption of euploid/aneuploid, one could combine as p(x₁, x₂, x₃,x₄|a)g(y|a) and p(x₁, x₂, x₃, x₄|e)g(y|e) and then multiply each by theprior p(a) and p(e) given the maternal age. One could then choose theone that is highest.

In one embodiment it is possible to evoke central limit theorem toassume distribution on g(y|a or e) is Gaussian, and measure mean andstandard deviation by looking at multiple samples. In anotherembodiment, one could assume they are not independent given the outcomeand collect enough samples to estimate the joint distribution p(x₁, x₂,x₃, x₄|a or e).

In one embodiment, the ploidy state for the target individual isdetermined to be the ploidy state that is associated with the hypothesiswhose probability is the greatest. In some cases, one hypothesis willhave a normalized, combined probability greater than 90%. Eachhypothesis is associated with one, or a set of, ploidy states, and theploidy state associated with the hypothesis whose normalized, combinedprobability is greater than 90%, or some other threshold value, such as50%, 80%, 95%, 98%, 99%, or 99.9%, may be chosen as the thresholdrequired for a hypothesis to be called as the determined ploidy state.

Free-Floating DNA of Children from Previous Pregnancies in MaternalBlood

One difficulty to non-invasive prenatal diagnosis is differentiating DNAin the maternal blood from the current pregnancy and from previouspregnancies. Some believe that genetic matter from prior pregnancieswill go away after some time, but conclusive evidence has not beenshown. In one embodiment of the present disclosure, it is possible todetermine fetal DNA present in the maternal blood of paternal origin(that is, DNA that the fetus inherited from the father) using thePARENTAL SUPPORT™ (PS) method, and the knowledge of the paternal genome.This may utilize phased parental genetic information. It is possible tophase the parental genotype from unphased genotypic information usinggrandparental genetic data (such as measured genetic data from a spermfrom the grandfather), or genetic data from other born children, or asample of a miscarriage. One could also phase unphased geneticinformation by way of a HapMap-based phasing, or a haplotyping ofpaternal cells. Successful haplotyping has been demonstrated byarresting cells at phase of mitosis when chromosomes are tight bundlesand using microfluidics to put separate chromosomes in separate wells.In another embodiment it is possible to use the phased parentalhaplotypic data to detect the presence of more than one homolog from thefather, implying that the genetic material from more than one child ispresent in the blood. By focusing on chromosomes that are expected to beeuploid in a fetus, one could rule out the possibility that the fetuswas afflicted with a trisomy. Also, it is possible to determine if thefetal DNA is not from the current father, in which case one could useother methods such as the triple test to predict genetic abnormalities.

Non-Invasive Gender Determinations

The methods described herein can be used for non-invasive genderdetermination at a very early gestational age, for example as early asfour week, as early as five weeks, as early as six weeks, as early asseven weeks, as early as eight weeks, as early as nine weeks, as earlyas ten weeks, as early as eleven weeks, and as early as twelve weeks.

Determining Whether Fetal Cells in Maternal Blood are from the CurrentPregnancy

Non-invasive prenatal diagnosis involves the ability to determine thegenetic state of a gestating fetus using non-invasive methods.Typically, this involves a blood draw from the mother, and the use ofgenetic material from the mother that may be found in the maternalblood, or some portion of the maternal blood. There may be other sourcesof fetal genetic material available via methods other than a blood draw.In the case of the fetal genetic material available in maternal blood,there are two main categories: (1) whole fetal cells, for example,nucleated fetal red blood cells, and (2) free floating fetal DNA. In thecase of whole fetal cells, there is some evidence that fetal cells canpersist in maternal blood for an extended period of time such that it ispossible to isolate a cell from a pregnant woman that contains the DNAfrom a child or fetus from a prior pregnancy. There is also evidencethat the free floating fetal DNA is cleared from the system in a matterof weeks.

One challenge is how to determine the identity of the individual whosegenetic material is contained in the cell, namely to ensure that themeasured genetic material is not from a fetus from a prior pregnancy. Inone embodiment of the present disclosure, the knowledge of the maternalgenetic material can be used to ensure that the genetic material inquestion is not maternal genetic material. There are a number of methodsto accomplish this end, including informatics based methods such asPARENTAL SUPPORT™, as described in this document or any of the patentsreferenced in this document.

In one embodiment of the present disclosure, the blood drawn from thepregnant mother may be separated into a fraction containing freefloating fetal DNA, and a fraction containing nucleated red blood cells.The free floating DNA may optionally be enriched, and the genotypicinformation of the DNA may be measured. From the measured genotypicinformation from the free floating DNA, the knowledge of the maternalgenotype may be used to determine aspects of the fetal genotype. Theseaspects may refer to ploidy state, and/or a set of allele identities.Then, individual nucleated red blood cells may be genotyped usingmethods described elsewhere in this document, and other referentpatents, especially those mentioned in the first section of thisdocument. The knowledge of the maternal genome would allow one todetermine whether or not any given single blood cell is geneticallymaternal. And the aspects of the fetal genotype that were determined asdescribed above would allow one to determine if the single blood cell isgenetically derived from the fetus that is currently gestating. Inessence, this aspect of the present disclosure allows one to use thegenetic knowledge of the mother, and possibly the genetic informationfrom other related individuals, such as the father, along with themeasured genetic information from the free floating DNA found inmaternal blood to determine whether an isolated nucleated cell found inmaternal blood is either (a) genetically maternal, (b) genetically fromthe fetus currently gestating, or (c) genetically from a fetus from aprior pregnancy.

Some Embodiments

In some embodiments of the present disclosure, a method for determiningthe ploidy state of one or more chromosome in a target individual mayinclude any of the following steps, and combinations thereof:

Amplification of the DNA, a process which transforms a small amount ofgenetic material to a larger amount of genetic material that contains asimilar set of genetic data, can be done by a wide variety of methods,including, but not limited to, Polymerase Chain Reaction (PCR), ligandmediated PCR, degenerative oligonucleotide primer PCR, MultipleDisplacement Amplification, allele-specific amplification techniques,Molecular Inversion Probes (MIP), padlock probes, other circularizingprobes, and combination thereof. Many variants of the standard protocolmay be used, for example increasing or decreasing the times of certainsteps in the protocol, increasing or decreasing the temperature ofcertain steps, increasing or decreasing the amounts of various reagents,etc. The DNA amplification transforms the initial sample of DNA into asample of DNA that is similar in the set of sequences, but of muchgreater quantity. In some cases, amplification may not be required.

The genetic data of the target individual and/or of the relatedindividual can be transformed from a molecular state to an electronicstate by measuring the appropriate genetic material using tools and ortechniques taken from a group including, but not limited to: genotypingmicroarrays, and high throughput sequencing. Some high throughputsequencing methods include Sanger DNA sequencing, pyrosequencing, theILLUMINA SOLEXA platform, ILLUMINA's GENOME ANALYZER, or APPLIEDBIOSYSTEM's 454 sequencing platform, HELICOS's TRUE SINGLE MOLECULESEQUENCING platform, HALCYON MOLECULAR's electron microscope sequencingmethod, or any other sequencing method. All of these methods physicallytransform the genetic data stored in a sample of DNA into a set ofgenetic data that is typically stored in a memory device en route tobeing processed.

Any relevant individual's genetic data can be measured by analyzingsubstances taken from a group including, but not limited to: theindividual's bulk diploid tissue, one or more diploid cells from theindividual, one or more haploid cells from the individual, one or moreblastomeres from the target individual, extra-cellular genetic materialfound on the individual, extra-cellular genetic material from theindividual found in maternal blood, cells from the individual found inmaternal blood, one or more embryos created from (a) gamete(s) from therelated individual, one or more blastomeres taken from such an embryo,extra-cellular genetic material found on the related individual, geneticmaterial known to have originated from the related individual, andcombinations thereof.

In some embodiments, a set of at least one ploidy state hypothesis maybe created for each of the chromosomes of interest of the targetindividual. Each of the ploidy state hypotheses may refer to onepossible ploidy state of the chromosome or chromosome segment of thetarget individual. The set of hypotheses may include some or all of thepossible ploidy states that the chromosome of the target individual maybe expected to have. Some of the possible ploidy states may includenullsomy, monosomy, disomy, uniparental disomy, euploidy, trisomy,matching trisomy, unmatching trisomy, maternal trisomy, paternaltrisomy, tetrasomy, balanced (2:2) tetrasomy, unbalanced (3:1)tetrasomy, other aneuploidy, and they may additionally involveunbalanced translocations, balanced translocations, Robertsoniantranslocations, recombinations, deletions, insertions, crossovers, andcombinations thereof.

In some embodiments, the knowledge of the determined ploidy state may beused to make a clinical decision. This knowledge, typically stored as aphysical arrangement of matter in a memory device, may then betransformed into a report. The report may then be acted upon. Forexample, the clinical decision may be to terminate the pregnancy;alternately, the clinical decision may be to continue the pregnancy. Insome embodiments the clinical decision may involve an interventiondesigned to decrease the severity of the phenotypic presentation of agenetic disorder, or a decision to take relevant steps to prepare for aspecial needs child.

In one embodiment of the present disclosure, any of the methodsdescribed herein may be modified to allow for multiple targets to comefrom same target individual, for example, multiple blood draws from thesame pregnant mother. This may improve the accuracy of the model, asmultiple genetic measurements may provide more data with which thetarget genotype may be determined. In one embodiment, one set of targetgenetic data served as the primary data which was reported, and theother served as data to double-check the primary target genetic data. Inone embodiment, a plurality of sets of genetic data, each measured fromgenetic material taken from the target individual, are considered inparallel, and thus both sets of target genetic data serve to helpdetermine which sections of parental genetic data, measured with highaccuracy, composes the fetal genome.

In some embodiments the source of the genetic material to be used indetermining the genetic state of the fetus may be fetal cells, such asnucleated fetal red blood cells, isolated from the maternal blood. Themethod may involve obtaining a blood sample from the pregnant mother.The method may involve isolating a fetal red blood cell using visualtechniques, based on the idea that a certain combination of colors areuniquely associated with nucleated red blood cell, and a similarcombination of colors is not associated with any other present cell inthe maternal blood. The combination of colors associated with thenucleated red blood cells may include the red color of the hemoglobinaround the nucleus, which color may be made more distinct by staining,and the color of the nuclear material which can be stained, for example,blue. By isolating the cells from maternal blood and spreading them overa slide, and then identifying those points at which one sees both red(from the Hemoglobin) and blue (from the nuclear material) one may beable to identify the location of nucleated red blood cells. One may thenextract those nucleated red blood cells using a micromanipulator, usegenotyping and/or sequencing techniques to measure aspects of thegenotype of the genetic material in those cells.

In one embodiment, one may stain the nucleated red blood cell with a diethat only fluoresces in the presence of fetal hemoglobin and notmaternal hemoglobin, and so remove the ambiguity between whether anucleated red blood cell is derived from the mother or the fetus. Someembodiments of the present disclosure may involve staining or otherwisemarking nuclear material. Some embodiments of the present disclosure mayinvolve specifically marking fetal nuclear material using fetal cellspecific antibodies.

There are many other ways to isolate fetal cells from maternal blood, orfetal DNA from maternal blood, or to enrich samples of fetal geneticmaterial in the presence of maternal genetic material. Some of thesemethods are listed here, but this is not intended to be an exhaustivelist. Some appropriate techniques are listed here for convenience: usingfluorescently or otherwise tagged antibodies, size exclusionchromatography, magnetically or otherwise labeled affinity tags,epigenetic differences, such as differential methylation between thematernal and fetal cells at specific alleles, density gradientcentrifugation succeeded by CD45/14 depletion and CD71-positiveselection from CD45/14 negative-cells, single or double Percollgradients with different osmolalities, or galactose specific lectinmethod.

In one embodiment of the present disclosure, the target individual is afetus, and the different genotype measurements are made on a pluralityof DNA samples from the fetus. In some embodiments of the presentdisclosure, the fetal DNA samples are from isolated fetal cells wherethe fetal cells may be mixed with maternal cells. In some embodiments ofthe present disclosure, the fetal DNA samples are from free floatingfetal DNA, where the fetal DNA may be mixed with free floating maternalDNA. In some embodiments, the fetal DNA may be mixed with maternal DNAin ratios ranging from 99.9:0.1% to 99:1%; 99:1% to 90:10%; 90:10% to50:50%; 50:50% to 10:90%; or 10:90% to 1:99%; 1:99% to 0.1:99.9%.

In one embodiment, the method may be used for the purpose of paternitytesting. For example, given the SNP-based genotypic information from themother, and from a man who may or may not be the genetic father, and themeasured genotypic information from the mixed sample, it is possible todetermine if the genotypic information of the male indeed representsthat actual genetic father of the gestating fetus. A simple way to dothis is to simply look at the contexts where the mother is AA, and thepossible father is AB or BB. In these cases, one may expect to see thefather contribution half (AA|AB) or all (AA|BB) of the time,respectively. Taking into account the expected ADO, it isstraightforward to determine whether or not the fetal SNPs that areobserved are correlated with those of the possible father.

One embodiment of the present disclosure could be as follows: a pregnantwoman wants to know if her fetus is afflicted with Down Syndrome, and/orif it will suffer from Cystic Fibrosis, and she does not wish to bear achild that is afflicted with either of these conditions. A doctor takesher blood, and stains the hemoglobin with one marker so that it appearsclearly red, and stains nuclear material with another marker so that itappears clearly blue. Knowing that maternal red blood cells aretypically anuclear, while a high proportion of fetal cells contain anucleus, he is able to visually isolate a number of nucleated red bloodcells by identifying those cells that show both a red and blue color.The doctor picks up these cells off the slide with a micromanipulatorand sends them to a lab which amplifies and genotypes ten individualcells. By using the genetic measurements, the PARENTAL SUPPORT™ methodis able to determine that six of the ten cells are maternal blood cells,and four of the ten cells are fetal cells. If a child has already beenborn to a pregnant mother, PARENTAL SUPPORT™ can also be used todetermine that the fetal cells are distinct from the cells of the bornchild by making reliable allele calls on the fetal cells and showingthat they are dissimilar to those of the born child. Note that thismethod is similar in concept to the paternal testing embodiment of thepresent disclosure. The genetic data measured from the fetal cells maybe of very poor quality, containing many allele drop outs, due to thedifficulty of genotyping single cells. The clinician is able to use themeasured fetal DNA along with the reliable DNA measurements of theparents to infer aspects of the genome of the fetus with high accuracyusing PARENTAL SUPPORT™, thereby transforming the genetic data containedon genetic material from the fetus into the predicted genetic state ofthe fetus, stored on a computer. The clinician is able to determine boththe ploidy state of the fetus, and the presence or absence of aplurality of disease-linked genes of interest. It turns out that thefetus is euploidy, and is not a carrier for cystic fibrosis, and themother decides to continue the pregnancy.

In another embodiment, a couple where the mother, who is pregnant, andis of advanced maternal age wants to know whether the gestating fetushas Down syndrome, Turner Syndrome, Prader Willi syndrome, or some otherchromosomal abnormality. The obstetrician takes a blood draw from themother and father. The blood is sent to a laboratory, where a techniciancentrifuges the maternal sample to isolate the plasma and the buffycoat. The DNA in the buffy coat and the paternal blood sample aretransformed through amplification and the genetic data encoded in theamplified genetic material is further transformed from molecularlystored genetic data into electronically stored genetic data by runningthe genetic material on a SNP array to measure the parental genotypes.The plasma sample is may be further processed by a method such asrunning a gel, or using a size exclusion column, to isolate specificsize fractions of DNA; specifically, molecules of DNA that are shorterthan 500 bases are isolated. The mixture of short DNA fragments isprepared into a DNA library suitable for sequencing. The preparation mayinvolve preferential enrichment of certain polymorphic alleles. Thepreferential enrichment may involve hybrid capture techniques, PCR basedselective amplifications techniques, circularizing probe based targetingtechniques, or other targeting techniques. Other methods may be used toenrich the fraction of fetal DNA in the sample. The DNA may then besequenced using a high throughput sequencing method, for example, usingthe ILLUMINA GAIIx GENOME ANALYZER. The sequencing transforms theinformation that is encoded molecularly in the DNA into information thatis encoded electronically in computer hardware. An informatics basedtechnique that includes the presently disclosed embodiments, such asPARENTAL SUPPORT™, may be used to determine the ploidy state of thefetus. It is determined that the fetus has Down syndrome. A report isprinted out, or sent electronically to the pregnant woman'sobstetrician, who transmits the diagnosis to the woman. The woman, herhusband, and the doctor sit down and discuss the options. The coupledecides to terminate the pregnancy based on the knowledge that the fetusis afflicted with a trisomic condition.

In another embodiment, a pregnant woman, hereafter referred to as “themother” may decide that she wants to know whether or not her fetus(es)are carrying any genetic abnormalities or other conditions. She may wantto ensure that there are not any gross abnormalities before she isconfident to continue the pregnancy. She may go to her obstetrician, whomay take a sample of her blood. He may also take a genetic sample, suchas a buccal swab, from her cheek. He may also take a genetic sample fromthe father of the fetus, such as a buccal swab, a sperm sample, or ablood sample. He may send the samples to a clinician. The clinician mayenrich the fraction of free floating fetal DNA in the maternal bloodsample. The clinician may enrich the fraction of enucleated fetal bloodcells in the maternal blood sample. The clinician may use variousaspects of the method described herein to determine genotypic data ofthe fetus. That genotypic data may include the ploidy state of thefetus, and/or the identity of one or a number of alleles in the fetus. Areport may be generated summarizing the results of the prenataldiagnosis. The report may be transmitted or mailed to the doctor, whomay tell the mother the genetic state of the fetus. The mother maydecide to discontinue the pregnancy based on the fact that the fetus hasone or more chromosomal, or genetic abnormalities, or undesirableconditions. She may also decide to continue the pregnancy based on thefact that the fetus does not have any gross chromosomal or geneticabnormalities, or any genetic conditions of interest.

Another example may involve a pregnant woman who has been artificiallyinseminated by a sperm donor, and is pregnant. She is wants to minimizethe risk that the fetus she is carrying has a genetic disease. She hasblood drawn at a phlebotomist, and techniques described in thisdisclosure are used to isolate three nucleated fetal red blood cells,and a tissue sample is also collected from the mother and geneticfather. The genetic material from the fetus and from the mother andfather are amplified as appropriate and genotyped using the ILLUMINAINFINIUM BEADARRAY, and the methods described herein clean and phase theparental and fetal genotype with high accuracy, as well as to makeploidy calls for the fetus. The fetus is found to be euploid, andphenotypic susceptibilities are predicted from the reconstructed fetalgenotype, and a report is generated and sent to the mother's physicianso that they can decide what clinical decisions may be best.

In one embodiment, the raw genetic material of the mother and father istransformed by way of amplification to an amount of DNA that is similarin sequence, but larger in quantity. Then, by way of a genotyping methodthe genotypic data that is encoded by nucleic acids is transformed intogenetic measurements that may be stored physically and/or electronicallyon a memory device, such as those described above. The relevantalgorithms that makeup the PARENTAL SUPPORT™ algorithm, relevant partsof which are discussed in detail herein, are translated into a computerprogram, using a programming language. Then, through the execution ofthe computer program on the computer hardware, instead of beingphysically encoded bits and bytes, arranged in a pattern that representsraw measurement data, they become transformed into a pattern thatrepresents a high confidence determination of the ploidy state of thefetus. The details of this transformation will rely on the data itselfand the computer language and hardware system used to execute the methoddescribed herein, but is predictable if those contexts are known. Then,the data that is physically configured to represent a high qualityploidy determination of the fetus is transformed into a report which maybe sent to a health care practitioner. This transformation may becarried out using a printer or a computer display. The report may be aprinted copy, on paper or other suitable medium, or else it may beelectronic. In the case of an electronic report, it may be transmitted,it may be physically stored on a memory device at a location on thecomputer accessible by the health care practitioner; it also may bedisplayed on a screen so that it may be read. In the case of a screendisplay, the data may be transformed to a readable format by causing thephysical transformation of pixels on the display device. Thetransformation may be accomplished by way of physically firing electronsat a phosphorescent screen, by way of altering an electric charge thatphysically changes the transparency of a specific set of pixels on ascreen that may lie in front of a substrate that emits or absorbsphotons. This transformation may be accomplished by way of changing thenanoscale orientation of the molecules in a liquid crystal, for example,from nematic to cholesteric or smectic phase, at a specific set ofpixels. This transformation may be accomplished by way of an electriccurrent causing photons to be emitted from a specific set of pixels madefrom a plurality of light emitting diodes arranged in a meaningfulpattern. This transformation may be accomplished by any other way usedto display information, such as a computer screen, or some other outputdevice or way of transmitting information. The health care practitionermay then act on the report, such that the data in the report istransformed into an action. The action may be to continue or discontinuethe pregnancy, in which case a gestating fetus with a geneticabnormality is transformed into non-living fetus. The transformationslisted herein may be aggregated, such that, for example, one maytransform the genetic material of a pregnant mother and the father,through a number of steps outlined in this disclosure, into a medicaldecision consisting of aborting a fetus with genetic abnormalities, orconsisting of continuing the pregnancy. Alternately, one may transform aset of genotypic measurements into a report that helps a physician treathis pregnant patient.

In one embodiment of the present disclosure, the method described hereincan be used to determine the ploidy state of a fetus even when the hostmother, i.e. the woman who is pregnant, is not the biological mother ofthe fetus she is carrying.

Some of the math in the presently disclosed embodiments makes hypothesesconcerning a limited number of states of aneuploidy. In some cases, forexample, only zero, one or two chromosomes are expected to originatefrom each parent. In some embodiments of the present disclosure, themathematical derivations can be expanded to take into account otherforms of aneuploidy, such as quadrosomy, where three chromosomesoriginate from one parent, pentasomy, hexasomy etc., without changingthe fundamental concepts of the present disclosure. At the same time, itis possible to focus on a smaller number of ploidy states, for example,only trisomy and disomy. Note that ploidy determinations that indicate anon-whole number of chromosomes may indicate mosaicism in a sample ofgenetic material.

In some embodiments, the genetic abnormality is a type of aneuploidy,such as Down syndrome (or trisomy 21), Edwards syndrome (trisomy 18),Patau syndrome (trisomy 13), Turner Syndrome (45X0) Klinefelter'ssyndrome (a male with 2 X chromosomes), Prader-Willi syndrome, andDiGeorge syndrome. Congenital disorders, such as those listed in theprior sentence, are commonly undesirable, and the knowledge that a fetusis afflicted with one or more phenotypic abnormalities may provide thebasis for a decision to terminate the pregnancy, to take necessaryprecautions to prepare for the birth of a special needs child, or totake some therapeutic approach meant to lessen the severity of achromosomal abnormality.

All patents, patent applications, and published references cited hereinare hereby incorporated by reference in their entirety. While themethods of the present disclosure have been described in connection withthe specific embodiments thereof, it will be understood that it iscapable of further modification. Furthermore, this application isintended to cover any variations, uses, or adaptations of the methods ofthe present disclosure, including such departures from the presentdisclosure as come within known or customary practice in the art towhich the methods of the present disclosure pertain, and as fall withinthe scope of the appended claims.

What is claimed is:
 1. A method for determining the number of copies ofa chromosome or chromosome segment of interest in the genome of agestating fetus, the method comprising: hybridizing DNA in a mixedsample of DNA comprising fetal DNA and maternal DNA to a microarraycomprising a plurality of probes comprising a locus (i) that is known tobe polymorphic and (ii) that is likely to be informative based on therate of SNP heterozygosity in the human population for the locus;measuring a signal from DNA in the sample binding to each of the probesin the plurality of probes on the microarray to obtain measured geneticdata comprising the measured signal for each allele at the plurality ofpolymorphic loci on a chromosome or chromosome segment; calculating, ona computer, allele ratios at the plurality of polymorphic loci from themeasured signal for each allele at the plurality of polymorphic loci;creating a plurality of hypotheses specifying the number of copies ofthe chromosome or chromosome segment of interest in genome of the fetus;calculating, on a computer, expected allele ratios at each polymorphiclocus on the chromosome or chromosome segment for each hypothesis;calculating, on a computer, a confidence for at least one of thehypotheses using the expected allele ratios and the calculated alleleratios.
 2. The method of claim 1, wherein the sample has been isolatedfrom maternal blood.
 3. The method of claim 1, wherein the methodfurther comprises amplifying the DNA prior to the measuring step.
 4. Themethod of claim 1, wherein the method further comprises preferentiallyenriching the DNA at the plurality of polymorphic loci prior to thehybridization step.
 5. The method of claim 4, wherein the preferentiallyenriching the DNA at the plurality of polymorphic loci comprises:obtaining a pre-circularized probe such that the 3′ and 5′ ends aredesigned to hybridize to a region of DNA that is separated from thepolymorphic region of the allele by a small number of bases, where thesmall number is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, or 20, or a combination thereof; hybridizing thepre-circularized probe to purified DNA from the sample; circularizingthe pre-circularized probe; and amplifying some or all of thecircularized probe.
 6. The method of claim 4, wherein the preferentiallyenriching the DNA at the plurality of polymorphic loci comprises:obtaining a forward probe such that the 3′ end of the forward probe isdesigned to hybridize to the region of DNA immediately upstream from thepolymorphic region, and separated from the polymorphic region by a smallnumber of bases, where the small number is selected from the groupconsisting of 1, 2, 3, 4, 5, 6 to 10, and 11 to 20; obtaining a reverseprobe such that the 3′ end of the reverse probe is designed to hybridizeto the region of DNA immediately downstream from the polymorphic region,and separated from the polymorphic region by a small number of bases,where the small number is selected from the group consisting of 1, 2, 3,4, 5, 6 to 10, and 11 to 20; hybridizing the two probes to DNA in thesample of DNA; and amplifying the DNA using the polymerase chainreaction.
 7. The method of claim 4, wherein the preferentially enrichingthe DNA at the plurality of polymorphic loci comprises: obtaining a setof hybrid capture probes; hybridizing the hybrid capture probes to theDNA in the sample; and physically separating the hybridized DNA from thesample of DNA from the unhybridized DNA from the sample.
 8. The methodof claim 7, wherein the set of hybrid capture probes are designed tohybridize to a region that is flanking but not crossing the polymorphicallele.
 9. The method of claim 8, wherein the set of hybrid captureprobes are designed to hybridize to a region that is flanking but notcrossing the polymorphic allele, and wherein the length of the flankingcapture probe may be selected from the group consisting of as low asabout 25 bases.
 10. The method of claim 4, wherein the preferentialenrichment results in an average degree of allelic bias between thesample after preferential enrichment and the sample prior topreferential enrichment of a factor of no more than a factor of 1.2. 11.The method of claim 1, wherein the plurality of polymorphic locicomprise single nucleotide polymorphisms.
 12. The method of claim 1,wherein the step of determining the relative probability of eachhypothesis uses an estimated ratio of fetal to maternal DNA in thesample.
 13. The method of claim 1, comprising using maximum likelihoodestimates to select the hypothesis with the greatest probability. 14.The method of claim 1, wherein the probabilities of each of thehypotheses are calculated using statistical techniques taken from agroup consisting of a read count analysis, comparing heterozygosityrates, a statistic that is only available when parental geneticinformation is used, a probability of normalized genotype signals forcertain parent contexts, a statistic that is calculated using anestimated fetal fraction, and combinations thereof.
 15. The method ofclaim 1, further comprising producing a report stating the determinedconfidence for at least one of the hypotheses.
 16. A method fordetermining the number of copies of a chromosome or chromosome segmentof interest in the genome of a gestating fetus, the method comprising:obtaining a plurality primers to a locus (i) that is known to bepolymorphic and (ii) that is likely to be informative based on the rateof SNP heterozygosity in the human population for the locus; amplifyingDNA in a mixed sample of DNA comprising fetal DNA and maternal DNA usingthe plurality of primers to obtain amplified products comprising theplurality of polymorphic loci on a chromosome or chromosome segment;measuring an amount of the amplified products to obtain a measuredquantity of each allele at the plurality of polymorphic loci on thechromosome or chromosome segment; calculating, on a computer, alleleratios at the plurality of polymorphic loci from the measured quantityif each allele at the plurality of polymorphic loci; creating aplurality of hypotheses specifying the number of copies of thechromosome or chromosome segment of interest in genome of the fetus;calculating, on a computer, expected allele ratios at each polymorphiclocus on the chromosome or chromosome segment for each hypothesis;calculating, on a computer, a confidence for at least one of thehypotheses using the expected allele ratios and the calculated alleleratios.
 17. The method of claim 16, wherein the step of measuring theamount of the amplified products is performed by sequencing.
 18. Themethod of claim 16, wherein the method is executed for a plurality ofgestating fetuses, the method further comprising: determining thefraction of DNA that is fetal in each of the samples; and wherein thestep of measuring the amount of the amplified products is performed bysequencing a number of amplified DNA molecules from each of the samples,where more molecules of DNA are sequenced from those samples that have asmaller fraction of fetal DNA than those samples that have a largerfraction of fetal DNA.
 19. The method of claim 16, wherein the method isexecuted for a plurality of gestating fetuses, and where the measuringthe amount of the amplified products is performed, for each of thefetuses, by sequencing a fraction of the sample of DNA to give a firstset of DNA measurements, the method further comprising: making a firstrelative probability determination for each of the hypotheses for eachof the fetuses, given the first set of DNA measurements; resequencing asecond fraction of the sample from those fetuses where the firstrelative probability determination for each of the hypotheses indicatesthat a hypothesis corresponding to an aneuploid fetus has a significantprobability, to give a second set of DNA measurements; making a secondrelative probability determination for hypotheses for the fetuses usingthe second set of DNA measurements and optionally also the first set ofDNA measurements; and determining the number of copies of the chromosomeor chromosome segment of interest in the genome of a fetus whose samplewas resequenced by selecting the hypothesis with the greatestprobability as determined by the second relative probabilitydetermination.